Well, my friend and I auditioned the VAC 300 Phi stereo amp in his system. (He was looking to see how it compared to his hybrid Lamm M2.2 (220 wpc) monoblock amps. (The Lamm M2.2 amps have been the best fit with his Rockport Antares speakers that he has been able to find. The Rockports are a true full range speaker and need a lot of power. The Lamm's have a touch of tubes in the treble and mid-range, combined with a deep and tight bass response.) I will be completely honest and state that up until the VAC 300, I had never heard an amp that could compare to the Lamm M2.2, and that includes direct comparisons to:
The DarTZeel NHB 108,
The VTL MB 450,
The BAT 150,
The Kora Cosmos,
The Classe 401,
And a couple of others,
I can not state that one is better than the other, but both units have different strengths and weaknesses, (albeit their weaknesses are really just of the nitpicking type!). Both amps soundstage and image incredibly well, and as good or better than any amp I have ever heard. Neither adds any grain to the music at all. These are literally the two best amps I have ever heard.
(Note: Due to some of the music my friend and I like to listen to, (rock, and large symphonic pieces), we both have somewhat inefficient speakers, in order to get rock solid bass response, so neither of us have ever gotten into the SET type of amps.)
With that said, here are the differences between the two:
The mid-range and treble of the VAC unit was very lush, and wonderful to listen to. Listening to vocals on the VAC was a real treat due to the lushness of the mid-range. It is tough to actually say the VAC's mid-range was better than the Lamm, as the Lamm seemed a bit more neutral, but I will say that the VAC's mid-range was intoxicating nonetheless. (Six of one, half a dozen of the other!). However, the treble response was remarkably well extended and airy, and actually was slightly better than the Lamm. (Which was surprising, as I had never heard an amp better the Lamm before in the treble response.) However, the VAC's bass response was not quite as deep and tight as the Lamm's was. (It could be that this was due to the difference between the amps as the VAC is a stereo amp and the Lamm is a monoblock design, and the limited power supply of the VAC stereo unit may have come into play. That is my guess anyway.) In addition, on percussive instruments, it seemed that the VAC was slightly slower than the Lamm in presenting that initial attack. (Such as on drums, and even on piano key strokes.) It was not a lot, but it was definitely there. This is what kept both my friend from switching to the VAC, and what led to his friend ultimately selling the VAC.
(However, my friend seriously thought about buying the VAC just to listen to vocal music, it was that intoxicating. However it was just too expensive at the time to seriously contemplate.)
There was one other minor difference. The VAC ran really hot, raising the temperature in the room several degrees. The Lamm's ran really warm, so the room only raised the temperature a few degrees. (The Lamm does not get hot enough that you can not put you hand on the unit, but it is very warm to the touch.) This was another influencing reason my friend did not switch to the VAC, as his room is not air-conditioned.
So there you have my take on the similarities and differences between the two units. As I stated quite clearly, both of these amps are the best of the best, and you will have a tough time equaling the performance when, (and if), you decide to switch.
Good Luck!