There are some significant issues I think that people run into when we are talking about a portable music device.
1. Apple owns the market. The number two player is SanDisk - the market for 'high end' is going to be a tough one to break into.
2. I would make sure that the parent company is a member of CEDIA and that you check with CEDIA to see what sales figures they may have. They may be able to provide actual reported industry information.
3. Cel phones are what I think the portable industry is moving towards, and any potential tie-in to a cel phone could lead to major revenue return if done properly as part of marketing, but this is going to be a big time investment.
4. It WILL be a big time investment, because you will need to be able to differentiate your product in some manner. Audio is basically easy to portablize, so what will you give that makes it better? On the road, people already have access to FLAC players and other lossless players for the VERY few who care about that level of audio quality in a portable format.
5. Home media players aren't portable, and they hit the areas which include FLAC and WAV format files stored over LAN connections as well. (Popcorn Hour, DuneHD, etc.)
6. Incredible software, included with the product, is a bit more than lacking. iTunes stinks, other manufacturers just have you use the stuff built into your computer. So, finding a good and unique program might help, but once again - pricey.
I wouldn't think about going into the personal media player market at this point. There are way to many cheap imports and Apple is the God in the industry with the major kick of the iPhone likely going onto other networks by year's end.
I haven't touched my other players since I got an iPod, and I'm never intending to.
My custom installations are all based around iTunes and iPods.
Seriously - very tough call, though there is room for improvement, it is not as straightforward as just getting a product to market.