Sounds like you might have a mike/pa issue. All the talkbox is, as you probably already know, is a metal box with a speaker, plastic tube, and a bypass switch. So if you're having to crank your amp to get your mike to pick up the sound it might be:
1) bad mike/mike cable, etc
2) do you have the ohms matched up? I think the talk box [email protected]
3) What are you running the mike into? Do you have a mike pre, are you running into another amp? or a p.a board? It does matter, some mikes have much lower output than others and need a mike pre to boost the signal.
I regularly use a heil with a mesa triple recto into a P.A system with a SM 57, and have no problems with balance. It also depends on what kinda sound you want out of it as well. Do you want to use the heil as an accent or are you intending on using as a large part of your sound?
The heil isn't bad, but another company makes a self-power one, which seems like a good idea...but I can not remember right now which company it is...its not an obscure one to be sure. Hope that helps, at least gives ya some other tangents to go on to solve your problem. Good luck! Tobe