'sound' is in the ear of the beholder. The quality is limited by the analogue to digital coversions used to record the 'music' and the digital to analogue conversion to play it. These would be very similar if not identical for all machines, the main differances would be in the output stage and headphones this would make it very dificult to test. I havent seen a 'frequency test recording' for mp3's but if you search there may well be one.
When you are playing to the yoof market then size, look, features and brand name are more important. Look at the mobilephone adds, they almost struggle to mention actualy talking to people.
Prehaps you need to read reviews in 'The Gramophone'rather than PCA. I think a leakage test would be usefull, when I can hear the boomp boomp at 10 feet I think something is wrong.