If you are happy going to IEM the only reason for you to need an amp is for the few who are not. That's a bit strange.
I wouldn't mind betting there's at least one turkey playing way too loud in the lacking in-ears group.
I don't believe in half measures for bass amplification. Neither do I believe in catering to idiots, especially when there is PA. The bass that you make on stage messes with the front of house sound.
Plug your Helix into a clean power amp like a Quilter and a full range cab like a Barefaced. What comes out will be very close to a FOH sound.
For the love of bass, EQ the PA to the room before trying to EQ anything else.
Edit, I should have read the remainder of posts.
Since your PA is without bass bins aka subwoofers I can't imagine it is all that beefy in the kick or bass when it gets cranked up. You might be better playing to the room along with the drummer and leaving PA to vocals and all the other squawky parts.