What about the sound quality difference between the Rio Car and the Neo?

With this class of products, the sound quality is going to be more highly dependent upon your amplifiers/speakers/wiring/installation than in the playback unit itself. And of course, how well-made the MP3s are.

The empeg player supposedly has very high-quality DACs, it's been said that it's the best available in this class of product. Also, it has a fully parametric equalizer. This allows you to tweak the sound more than the other units.