I used to have the Carvin Quad; its two clean channels sounded great, the Carvin X100B is renowned for its outstanding cleans, but much of it comes from its power section too. The Quad lacks in the crunch ability, and depending on the unit you get, (the newer ones sound much better) and the tubes you use the high gain is either muddy or extreme, the latter being better of the two. I can't comment on the others for clean tones but the ADA MP1 Classic has an outstanding solid state clean tone, and a really nice stereo chorus, it's modeled after the Roland Jazz Chorus. I said the "Classic" because it has an added brown channel that has excellent crunch tones that the original doesn't have. The MP-1 is an iconic piece, it was widely used in the 80's and early 90's before grunge took over. It's tone is mainly a hot rodded Marshall, but does the crunch and clean just as well imo.
The Engl and Soldano aren't really known for their clean channels. Is it the Rectifier pre you're talking about, I hear it's outstanding, but not because of its cleans. Always wanted to try a VHT Valvulator
, so I can't say much about em. Same goes for the CAE and the Bogner, known much more for their distortion. I'm afraid only one of your choices has been noted for its clean channels.
Most importantly, read this thread, and when you get to the bottom, click the link to the
older thread. It will tell you how to get a decent power amp tone from the Axe Fx. {I just happen to read it the other day
}
New thread, 1 page:
https://forum.fractalaudio.com/threads/is-there-a-model-of-a-tube-power-amp.138663/#post-1644316
Old thread, 2 pages:
https://forum.fractalaudio.com/threads/is-it-possible-to-bypass-the-preamp.70487/
It took me a while to find these (got sidetracked a couple times, and then there was the whole China thing), but I found them, so please give them a look.