Personally I can't answer the question of how they compare to the SDS amps but I've had more than my fair share of amps in the system in the last few years and IMO none of them compare in terms of clarity and the sheer amount of musical information allowed through.
List of some in no particular order
Consonance 211 and 845 (SET TUBE)
Atma-Sphere M-60 (OTL Tube)
McIntosh MC275 (PP Tube)
Pass Labs XA30.5 (Class A SS)
Luxman M-600 (Class A SS)
Jolida Music Envoy (PP tube, 211 triodes)
Luxman SQ-38 integrated (PP tube)
nuforce ref 18 (class D)
Spectron Musician III mono's (class D)
ModWright KWA 150 mono's (class A/B ss)
Odyssey extreme mono's (class A/B ss)
Threshold SA50 (class A ss)
hot rodded Dynaco ST70 (pp tube)
Eastern Electric M156 mono's (pp tube)
Eastern Electric M88 integrated (pp tube)
R.E. Designs LNPA 150 (class A/B ss)
Audio Mirror 45W SET (tube SET)
A few others that I can't think of off hand. Yes, all in the same room with either my current speakers, GedLee Abbey, or the previous speakers, Meadowlark Blue Heron 2.
With or without the subs, these amps are in a class by themselves compared to any of the above. All of the above have strengths and weaknesses but for my tastes I'm keeping the little NC400's for the foreseeable future. Just my .02.
mike