It was determined that this needed to be posted here on AppleFritter as well in the event that there might be a 'FritterCritter poking around who may want to get involved. 
This is my post from 68kMLA:
This is a post I made on MacMod back before MacTech took over..then it turned into AppleCentral sometime when I was not looking. <_< >_>
I never got involved with MacTech but I want this here as well because it is useful information. (IMO anyway)I have a Syba SD-SATA-150R in my Digital Audio G4. It is a card that uses the Sil3512 chipset and like other Sil3512 cards with suitable eeprom, can be flashed with the wiebetech TCS1-1 firmware.
I know it can be flashed because there is a forum thread in another language based in another country that google translates very badly. It has a link to the firmware, a screenshot of System profiler with the card being used in OS X but as far as I recall I never read anything about booting off the card.(at least nothing translated into english)I was looking for something to do just now and I remembered that I wanted to see if my card was in fact bootable so I poked around on google for a bit to try and find what wiebtech cards were bootable in Macs.
Turns out the Sil3512 based WeibeTech TeraCard is in fact bootable. After verifying that I was actually using the same firmware as the bootable card, I booted my G4 off a Leopard install disc then installed to the SATA drive as a test.
It boots!This is incredibly awesome.
This is the card I got:
http://ncix.com/products/index.php?sku=33440&vpn=SD-SATA150R&manufacture=Syba
Others should work as well but not all. I have a Sil3512 based cheapo noname shady bargain-bin in Japan card and it seems that it cannot be flashed at all, even with DOS flashing programs. *shrug*Anyway, this is how I went about doing it.
Insert the card into Mac.
Boot up.
Run the flasher program.
Follow the prompts and select the Firmware option.(it looks like Firmware option = Mac and BIOS option = PC, I might be wrong, I did not extensively test aside from that if you use the BIOS option it is no longer usable in OS X)
Reboot
Check System Profiler for card recognition.
Shutdown and connect drive
Boot
????
PROFIT!
http://i27.tinypic.com/11h6ky8.png
To be fair, you might not need to do that extra reboot between flashing and connecting the drive. I just did not have the drive in my case at that point of testing.TCS1-1 flasher is here:
http://www.wiebetech.com/webtech.php?sfid=133&pcode=TC-PCIThe WiebeTech site says that this card should support hotswap but I do not recall having that work. So far I have had to connect my drives while my Mac was off for them to work. However, since it is bootable then I would want to boot off it simply because it means I can remove my older and more likely to fail PATA drive from the case and completely sidestep the LBA48 issue that forces me to partition my PATA HDD then use an enablery-mabob to access the rest of it.
Also of note. My Quicksilver 2002 would not initialize the video adapter or even chime with this card in it no matter what slot I put it in or what other cards are in it. According to the macgurus forum this is a known issue with some Silicon Image cards and some Digital Audios and Quicksilvers. It is not related to the WiebeTech firmware on the card or the fact that the card is flashed! Looks like at this point nobody knows the real cause, only that you need to try another card or another Mac.
With regard to the hotswap and non-boot issues.. YMMV.
Either way, this is frikkin great!It is about time we had this posted somewhere in english. ::)
I did later get a second Sil3512 card that also flashed well.
I need to mention, you cannot boot or otherwise use OS 9 or lower with Sil3512. At least not with this firmware. OS X only. Still though, great for G4s and G3s that run X only.
And a picture of one of my cards(they have slightly different layouts but the same chips):
I actually recently tried hotswapping on mine and it did work, even though previously I seem to recall it did not.. idk what the deal is but if it works for you then great. 
Also, my own experience with this card is limited to Mac OS 10.5 specifically.
As well as a followup post by Renegade in the same thread:
I'm happy to report that the card is recognized by 10.2 & 10.4 installers, and is bootable on my B&W G3.
So that is about that. In the PC world You see people crossflashing Sil3512 and Sil3112 cards so if you can only get one, you may still be in luck.
Not really sure what else I should add here, but if you have any questions or comments please do post. 
I'm confused... does that mean I can/should flash a 3512-based card with 3112 Mac firmware? Otherwise, where do I find 3512-compatible Mac firmware.
Sorry for the questions, but I'm considering a cheap 3512-based card for purchase.
My take, and I'm hoping Oelmuvun can confirm, is the 3512 can be Mac flashed but some, or all?, 3112-based cards have too small a flash chip to take a Mac bios.
The disadvantage of the 3512 is OS X only booting.
Sil3512 = we have usable Mac compatible firmware. (but OS X only)
Sil3112 = we only have firmware that /appears/ to be too big at this time. (OS 7 to OS X, if it can be made to work via bigger EEPROM or firmware reduction)
3512 firmware can go on 3112, at least in any cases I have heard of.
3112 firmware *should* be able to go on 3512, if EEPROM is small enough or we get a smaller dump from some other card.
Keep in mind that if you have a 3112 based Mac card it would be nice to know how big the EEPROM actually is so we can see if the flasher strips certain things from it before flashing or anything like that. But also, if you come across a 3112 card (non-SeriTek/1s2 and non-sonnet TSATA) with a really small firmware it would be nice to have a dump of that to use.
Interestingly perhaps, the PC 3512&3112 firmwares are not so crazy when it comes to size difference as far as I recall, it is just the firmtek 1s2 firmware.
someone needs to reduce the firmtek rom by removing the mac os x kexts from it..
they are the reason the rom is too big..
if someone could somehow get copies of the kexts from their own mac os x install
(i think it copies the kexts onto the osx installation??)
and somehow compare the raw file as hex to the 1s2 romfile even if we just removed the kexts (i think there are 2-3?)
then the file size would be big enough to fit on a smaller rom chip..
im sure that the actual mac os classic bootability is small enough to fit on a .5MBit chip
if not the .5, at least the 010 1MBit variety if we could somehow remove the extra mac os x binary data
another thing to note is the discovery of dougg3's from the Sil3112 datasheet (http://wiki.osdev.org/User:Quok/Silicon_Image_Datasheets) that the last 16 bits of the rom contain instructions to configure the silicon image chip itself and the main reason why u cant boot with it when flashed on a sil3512 chip may be entirely because its being configured improperly (with the config string for the 3112) if we could take the proper 16 bits at the end of a 3512 firmware and copy them to the existing 1s2 firmware
i think this is worth the time + effort to investigate
https://68kmla.org/forums/index.php?/topic/13557-sil3112-flashing-sata/?p=221554
http://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CB0QFjAA&url=http%3A%2F%2Fwww.verbatim.com.au%2Ftechnotes%2FSiI-PB-0023.pdf&ei=8G5EVL3sLsP_yQTzu4HoBg&usg=AFQjCNHA7QrDqqpzyY2y0ITD_WKX-GGKGg&bvm=bv.77648437,d.aWw&cad=rja
one other thing to note is another discovery by dougg3 that the correct spelling of the card is actually "s i i" with the second i being capitalized... even though many many people write this as s i L aswell.. a common mistake, but when searching with google it might be best to use (SiI3112|Sil3112) both spellings.