Skip the PowerCab entirely - it is not up to par at all. Honestly, not a good product tonally.
Here are two options that will totally transform your experience -
a) Instead of using ""FRFR"", get a good guitar cab (with good guitar speakers of your choice). Also obtain a solid-state power amp and disable cab modeling / IR entirely on the Helix - run out via the SS power amp to the guitar cab. You will not believe your ears - it is to me, extremely close to an actual amp (I bet 99% would fail a blind test) and sounds SO much better than ""FRFR"".
b) If you don't want to go the above route, get a L6 Catalyst - don't use any of the onboard amps, run your Helix into the Catalyst (again with cab modeling disabled) using the Poweramp-In option. This doesn't sound as good as a) but is still a very good option and IMHO, FAR superior to ""FRFR"".
A 100W Catalyst is now just $199 direct from L6
Keep in mind if you're using a guitar cab or the Catalyst, room position and room matter
big time because of how the sound disperses. So make sure you're playing in a well-treated room / environment. If you play this way, all the beautiful and subtle details of the amp modeling really get highlighted. I can assure you that your problems aren't related to the amp modeling, which is extremely accurate on most modern modelers. Rather, it's the audio reproduction device that's the problem.