MASSDEFECT
Member
The easy answer is that it depends on the tube power amp and the sims you are running really. If it's a really clean tube power amp like a vht 2/90/2, you can run pre and power amp sims on. it has tons of headroom and the kt tubes help. you can crank it up so loud and it wouldn't have any power tube distortion. But with a mesa simulclass, you can still get that mesa flavor no matter your volume.
As for using tube amps and plugging into the effects loop for their power amp. The common practice is to turn power amp sims off so as to not double the sag coming from the tube power amp. But some power sections of tube amps have also tons of headroom and are clean that running power amp sims on with the ax8 would also sound good. I find that amps that depend on preamp distortion have really nice power amp sections. That's why you see a lot of people running axe fx through an EVH 5150.
As for the preamp sims on the ax8/axe fx, some don't sound good running just as as pre amp sim. The marshall sims sound weird without the virtual tubes running because the whole sim hinges on the interaction between the preamp and the master.
As for using tube amps and plugging into the effects loop for their power amp. The common practice is to turn power amp sims off so as to not double the sag coming from the tube power amp. But some power sections of tube amps have also tons of headroom and are clean that running power amp sims on with the ax8 would also sound good. I find that amps that depend on preamp distortion have really nice power amp sections. That's why you see a lot of people running axe fx through an EVH 5150.
As for the preamp sims on the ax8/axe fx, some don't sound good running just as as pre amp sim. The marshall sims sound weird without the virtual tubes running because the whole sim hinges on the interaction between the preamp and the master.