Any benefit from" same brand" amp/pre-amp??

'd' amps may be said to have problems with hi frequencies, especially with low impedance loads...at those frequencies. The output zobel is the cause.

Look up the info on the top B&O ASP 1000 module as used by Bel Canto and many others.

http://www.icepower.bang-olufsen.com/files/solutions/icepower1000asp.pdf

It's pretty much all done at 30khz, into 4 ohms.

LF problems? Tell that to literally dozens of Sub Makers!

To UNSOUND: I am not sure why the TAS reviewer made that claim: (see TAS issue 203--July August 2010); I am not as techically hip to challenge the claim and also may have misinterpreted his statement..... However, there is an internet audio dealer who offers 2 separate levels of upgrade to the Quad 909 amp which is said to improve the bass; but the upgraded versions are not inexpensive---there is approx a $300 upcharge to go to level 2; I think Quad would probably invalidate the warranty of "new" pieces that were modified. For the record, I have a pair of Acoustic Zen Adagios. Thanks Jim

Sunnjim, perhaps it's something peculiar to that Quad amp. Most seem to feel that with the right speakers, that bass response is a strong suit of some Class D amps.

Magfan, I very well could be missing something here, but why would one care much about what goes on at 30Khz?

Magfan made his point clear. Who cares even above 16kHz?
I use for 7 years Sunfire SRA class T amp which is an advance from class D technology with addition of sigma-delta signal encoding/decoding and found it superior to famous Wyred4Sound models.