After years of trying to make a guitar (tube) amp work as a stage monitor I finally joined the 21st century (frfr monitor) & cannot believe the difference. When I first got the Helix I used a channel switching amp (clean / dist) straight in, then 4CM (fought the noise) but Friday gigs going straight from work forced me to downsize; started using amp/cab sims to FOH, 1/4" to a Fender Pro Junior because it's small and simple; one vol, tone knob.
Never could really get it to sound right, even after using a split block with parametric EQ to notch out the offending frequencies. I also tried:
Blues Jr
Marshall (straight in & return)
Mesa Boogie " " "
Blackstar EL34 10W single ended
I thought what the heck, for $250 I got a small (8" with a tweeter horn) floor monitor thing and I'm blown away. Everytime I get a new amp I always break in the speaker with two things, Allman Bros Live at the Fillmore and Steely Dan Aja. When I started the Aja CD I couldn't believe my ears - it sounded better than my Stereo!
So then I plugged in and played clean then hard stuff- Deacon Blues to Mississippi Queen both sounded amazing, and I haven't even considered mic/line level or EQ! Some of our songs require controlled feedback- that works too! Wish I'd done this years ago. At 66 in a cover band this simplifies my life...
TL/DR: Try an FRFR monitor for stage wash if using a "real" amp doesn't work sonically. I've been blessed with some really great amps at home but for Helix this is a game changer.