Well, it sounds like your dedicateds are already in so they're probably wired with the minimum 10 AWG - no point redoing them. I don't know how your panel is laid out but I hope #1 and #3 are on the same side of the neutral. If not (or you can't change them,) then use one circuit for amps and the other for front end stuff.
Why do you have two EP units? I have an SP (for front end) working off an EP (feeds the SP and the amps) but I live in an apartment w/ just 1 20A circuit.
Like I said, no need to go to 8AWG now unless you want to change everything all the way back to the breakers. It's just that you get a voltage drop over such long runs unless you go up a size. The downside is that most receptacle hardware (except for the clamping gas-tight hospital types) won't accept 8AWG wire. Stranded is easier to bend, etc. Solid is easier to connect.
Anyway, back to my elegant solution (I'm an anal retentive architect). If you want to do it right, remove a row of tiles from the wall box to a spot on the floor between the amps. Saw cut a 3" wide trench in the slab, install wire and conduit and terminate with a nice floor outlet box with one of those flush brass covers. OR, if you don't wan to remove the tile, (and don't mind bending the code a little) just saw cut a 3/4" groove along one of the tile grout lines, jamb some Romex into it and regrout. Make a pocket for the floor receptacle using concrete drills and chisels and grout it in. I know it sounds like a hassle, but it's so nice when you do it right!