I run a Helix LT and a Katana 100. The idea was playing a gig, the Helix straight in is the plan. The Katana 100 I use for practicing at home with the Helix, or as a backup to the Helix if it were to go down, the Katana 100 + GA-FC would get me by.
I started by using the effects return to bypass the preamp and got pretty good results. But I've actually liked the sound more going straight in the front and using the acoustic setting, which I believe is supposed to be a full range mode on the Katana, so while not a FRFR, I think it is probably close enough for my purposes. Katana speaker generally benefits from getting broken in and generally sounds a little brittle initially.