As for stomps, there would be a few that would be nice to have. That's why I asked.
So specifics and samples are essential in your quest for tonal-blissdom. Can you provide examples (YouTube, SoundCloud, etc.) for us to build off of?
One thing to note about the FAS gear is not to get to tied up on the amp/drive/cab/fx blocks verbatim for what you are trying to replicate. Sometimes, other models that you would not traditionally procure in the 'real amp' world will get you
precisely the tone you are looking for. What I am getting at is that you are used to a Mesa Mark IV model 2x12/4x12/other setup in person with a tubescreamer or other drive in front of it (guessing). The FAS gear is a versatile piece of gear that's range of accuracy is
pretty close on most things as you noted. Ultimately,
try new things, amps, drives that you would
not traditionally try in person to re-evaluate your tone. If you're looking for a heavy Mesa tone, try the ENGL Severe with a TS808 pedal out front to push it in a small signal chain DRIVE (TS808) > AMP (Severe) > CAB (4x12 Greenback) from I > O.
Most important is to start simple and take note of what you are referencing with (monitors, FRFR, etc.). You are simulating a recorded version of an amp and cab combo, there will be limitations yet endless opportunity. Frame of reference is important in getting you to where you want to be.
Ian, I am assuming people jumped on the 'Klon' comment which initially peaked my curiosity in this thread. I just wanted to ensure sincerity in the request for a Mark IV rig setup in the FAS lineup.
Hope that helps, looking forward to assisting anyway possible, thanks.