Thunderbird custom new mail wav

Since I absolutely despise Mail.app, I have been using Thunderbird for a while with both my IMAP and POPP3 email accounts. I discovered the new mail notification .wav sound option in the preferences window, but I cannot get it to work with any wavs I have They open in Quicktime and I have tried converting them to a different frequency in Quicktime Pro but it still fails to work. Any ideas?