For several years, I've enjoyed a PS Audio BHK preamp (which uses tubes in the input stage) along with a pair of M700 monoblocks. They were driving Thiel CS2.2 speakers, and they sounded great. Before I used the BHK pre, though, I had to be careful with the Thiels sounding a little too bright on certain recordings or with hyper-detailed cables.
A couple of months ago, I decided to try a different Class D amp, specifically the Atma-Sphere Class D GaNFET monoblocks. I've been really impressed with the transparency and mid/high frequency smoothness of the A-S amps, which has been achieved without exaggerating sibilance or harshness. The soundstage width and depth has been amazing, with great layering and separation of instruments and singers. The A-S monos also provide solid, impactful bass, although break-in on the lower frequencies has been a bit slower than for the upper frequencies.
I've found that that gain for the A-S monoblocks has been a bit lower than the gain of the M700s, but this has not been a problem and I'm now able to use a wider range of volume settings on the BHK preamp. Fortunately, the A-S amps are extremely quiet even at higher volume settings.
An even more recent change in my system has been a change from the Thiel 2.2s to the PS Audio Aspen FR10 speakers. The FR10s and the A-S monoblocks are sounding great together. The level of transparency without harshness is amazing, which speaks to the synergy between the FR10's planar magnetic tweeter and midrange combined with the speed, low distortion, and finesse of the A-S GaNFETs. Recordings are sounding very real and engaging. And my new A-S/BHK/FR10 combination can "rock out" at fairly high sound levels when needed.
