My guess is and guess only, you were probably listening to files that were 16/44 or better in the store demo and at home you might be using 320k or so now. There is a noticeable quality difference. The above suggstions from the other 2 guys will get you going. I'd download foobar 2000 also, it runs smooth and tells you what resolution and bit rate the files are that are playing. Also, you didn't say, but I guarantee your store demo used some sort of DAC. What about you? Night and day improvement there.
Good Luck, Tim
Good Luck, Tim