One more question though, is there any particular music which would potentially sound better as a hi-res file? I have quite a lot of electronica, but will download something that is most likely to highlight any differences.
To make a reasoned assessment I'd choose something you can hear in real-life, and recorded in a normal acoustic (not a creation of the engineer's head). Personaly I'd consider a grand piano, or vocal with small group (say, guitar, bass, drums). Or an orchestra, assuming you've heard one in concert conditions.
In Linn terms, that means the likes of Artur Pizzaro, Claire Martin, Caiol Kidd, Sir Charles Mackerras/SCO, for example.
Listen not just to the tonal qualty, but more particularly, the naturalness of the reverberation, the decay, etc.