"play as background music on our website."

Don't... most people out here are still not comfotable with sound coming at them unbidden from web sites... I know I can't turn web-site audio off quickly enough.... Instead assemble a clips page where people can go and click each sample that they want to hear...

" convert the files to MP3s"
I have yet to find a format that JetAudio won't convert...   But it's more than just an audio converter... it's a whole media suite...

Good luck eh!