Luckily there are thousands of MOD files readily available (from ST and Amiga) and one can use Neo-Tracker to convert them into NEO format (convert from 16Bit stereo into 8Bit stereo).
Actually, the MODules have already 8bit samples. Some players convert the samples to 4bit to save space if Pokey is used for playback, but the Covox is 8bit natively.
The sound quality is pretty good, BTW. Unfortunatelly, many MODules are not replayed correctly or sometimes loaded at all. However, the wider spread of the Covox may encourage some people to release new and enhanced players.