Hello KeithR, I have had the original M625 in my system, which was very lovely, but not M625 S2... According to all reports I have read/heard, S2 is sonically quite enhanced over the original version. According to some, M625 S2 stereo and M725 monos might be the most refined pure power amps that Jeff designed. Below the list of enhancments in M625 S2 provided by the factory:
"We have taken the existing circuit topology and improved the important distortion specification at higher frequencies (above 2kHz) to a virtually unmeasureable level extending beyond 20 kHz .
This was accomplished with an innovative error correction technique previously unknown, or never implemented in the art of amplifier design.
The S2 incorporates a new custom designed input transformer and linear phase low pass filter for improved input signal buffering and EMI immunity.
Gold plated Cardas XLR input connectors with Rhodium contacts and teflon insulation provides a visually distinguishing appearance from the original 625 and provides improved signal integrity.
The S2 amplifier incorporates ceramic Rogers circuit board material for reduced dielectric energy storage.
The S2 Power Factor Corrected regulated Power supply improves upon the original 625 by incorporating Jensen four-pole capacitors which offers nearly an order of magnitude
reduction of output impedance and noise suppression. The power supply output voltage has been increased slightly to yield a 25 watt increase in total amplifier power output."
...
Your question about warmth is very interesting. From a frequency band extension and linearity, I would say that Rowland's curreent goal is neutrality more than ever, in the sense that there does not appear to be a preferential treatment of any particular region of the band. What rather has been happening in the last several years is a dramatic loweering of distortive artifacts, increase in harmonic complexity, and sensitivity in very low level detail.
The old early class D designs like M201, M501, and in some sense M525, could be accused of sounding matter of fact, and perhaps even sterile. I remember auditioning M201 and M501at Stereo Exchange and RMAF... The word "immersive" and "warm" certainly did not apply. The presentation was somewhat matter of fact and unemotional, even tiring. Even the original Continuum 500 integrated did not seem to elicit the use of the words "warmth" and "emotional".
But what Rowland has done in later years, including the devices that I have had in my system like M312, M625, M725, M535, M925, and now Daemon, bring back to me the emotion of my old M7 from the classic Rowland days, but with the resolution and transparency possible today.
So, to make a long story short, while current Rowland amps are not strictly speaking "warm" in the sense of having a preferential hump in the lower midrange and upper bass with a corresponding filtering of high treble, they have an immersive sound that some will call "organic", others will call "warm", and I instead call "immersive" and "congruent" with the sound of live acoustic instruments and human voices.
BTW, Rowland is preparing to release a new major product.... I'll post here as soon as I receive meaningful details from the factory.
Saluti, Guido