All

None, except maybe the price but than again great things costs a lot of money.

I use these with chord's CPA-5000 reference preamp and b&w's 800D and i think these are simply one of the best amps money can buy if not the best, loads of finesse with power, i don't know how they do it!
Very musical, the crescendo's in music can make you fall from the chair.

Similar Products Used:

Chord SPM-5000, Chord SPM-1200B, Chord SPM-1000B, Musical Fidelity Nu-vista