Ampzilla 2000 v2 and Mcintosh MC402

MC402 because you already have a McIntosh preamp. The MC402 will have a better resale value. The GAS company is out of business, so no warranty repairs.

@jasonbourne52 They are still in business under SST. I just spoke to the owner yesterday. In fact, I am purchasing the 2000 directly from the company.

... and I actually found out (to my surprise) that Mcintosh preamp goes well with other branches of amplifiers. I come to that realization after selling my MC352 amp and connecting the C1100 to my Pass Lab x150.5

I can’t tell you how the Ampzilla will compare to the McIntosh amp, but they are very good. I have owned many amps in that price range and the Ampzilla is one of the best. It’s nice that they are cool running and can deliver the amount of power they do without having to have a 20 amp outlet. They provide great detail and dynamics. I think they will tick the boxes for the things you mentioned you like, except maybe the "airy" high. I’m not sure I would describe it that way. I think the treble response is pretty neutral. To me, "airy" means something artificial added to the sound, but adjectives can be misinterpreted.

There is a lot of owner feedback that you can find with a search. I don’t remember reading anything negative about them before I bought mine.

If you are already purchasing the Ampzilla, why did you bother to ask the question?  Seems like you already answered it yourself.