x10V3 Tube buffer: Class A Sound or dud?

Actually it depends is my answer.

I bought the MF Xdac v3 and X-10v3 buffer a couple of years ago. Auditioned them in the dealers listening room. The X-10 made a huge instant difference (fuller, rounder sound, more detail).

Got it home and it still made a big difference (Audio alchemy digital drive 1.1, Linn LK1/2 and Martin logan SL3).

Most recently upgraded the amplification. Rogue Perseus tube pre, Spectron Musician 3 with remote sense cable. Now the X10 makes no almost no audible difference. Both my wife and I failed to pick it out consistantly listening to classical, rockk, or female vocal.

As I understand it tube buffer is meant to provide effortless drive / load to the DAC and Amp. Would it be expected that if the amp is easy to drive, the buffer would make no difference? Is there another explnation? It was an impressive difference in contribution between installation in 2 systems.

Next for review xPSU.

Tony