What's with the WAV/AIFF/FLAC upload requirement? Why don't you just accept mp3s?
It's all about maximizing flexibility for you and your fans. WAV, AIFF and FLAC are high-fidelity (lossless) formats. By starting with the highest possible quality source, we're able to convert your track into a bunch of different format and quality combinations, including MP3 (320, VBR), Ogg Vorbis, Apple Lossless, FLAC and AAC (aka .m4a or iTunes store format). Sure, most fans will just want the mp3 and won't know or care about anything else, but there's a rabid minority out there who'll love that you're giving them a choice. And if a new format/quality becomes à la mode (like when Amazon's mp3 store made iTunes' 128k AACs seem antiquated), we'll transcode to that too, without you having to do a thing.
Getting specific, your uploaded source material must be lossless, at least 16-bit/44.1kHz ("CD quality"). Higher quality sources are supported: 24-bit and 32-bit, with sample rates up to 192kHz (your FLAC-downloading fans will worship at your feet). We grudgingly accept mono material (you better have a good reason) but prefer stereo mixes, 2 channels max please (we don't know what to do with Sensurround).