Hi, Pete. I am guessing, that you have created your perfect tone specifically for your cab and not for FOH. I see two areas where that incosistency of Your tone is coming from:
1) I think the signal that goes via powerstage to the cab is stronger (u mentioned it is set to line level) than the signal that goes to FOH. That is why You hear more gain in the sound that is coming from your cab- You are pushing the ps170 harder, so it adds some distortion. Try changing Your signal level to the instrument level and tweak Your sound again (probably You will need more gain and stronger signal prior to Your amp model, then tweak low end and high frequencies, since they become stronger with the signal) untill You find Your perfect tone again and this time Your FOH sound should be closer to Your ps 170 plus cab tone.
2) I also think that your IR has different eq characteristics comparing to your cab, so try a different IR, that matches your cab better, and/or use an EQ block to match it further. Maybe even try making an IR yourself and use Your cab in the process.
The last thing is the quality of the FOH mixing board- they tend to sound very different, so maybe You could mic your cab with a real mic and then listen to the final sound that is coming from the FRFR speakers. Maybe that is just the nature of the mixing board/FRFR speakers You use.
Hope this helps.
Cheers,
Greg.
