Not heard a G55 but have heard a G57 at my local Dealer (Music Matters in Solihull). Seemed quite happy driving B&W 802s and some extremely expensive DynAudios. I use a 558.2 and a 559 in my system. The 559 is more powerful in wattage terms than the G57 but an older design. They reckon the G57 edges it on sound... which is really saying something. The 559 has an amazing dynamic range. The 558.2 is brilliant but noticeably less smooth than the 559. It is conversely twice as powerful (on paper) as the G55 but if it sounds better, it might be worth considering. Anyone know why the new amps are less powerful than their forebears ?

G98, HD621, 568.25, 558.2, 559, B&W 803Ds, HTM2D, 4xSCM1, ASW850, Pioneer PDLX5090 50" Plasma, Cables by Atlas and Chord