No good news here–you have to power it from the battery, or at least from a source capable of delivering 50 amps (like a main fuse panel, etc). Breakers on ACC switches are usually 15 amps, which you’ll trip constantly using that amp, and could likely damage the switch, breaker, and switchpanel wiring.
The even worse news is if you want to use nice, fat, marine-grade tinned copper wire two 12-ish-foot strands are probablly gonna cost you close to as much as the amp did in the first place. Otherwise, you can get the 61 cent per foot stuff at Lowes.
Also, I don’t recommend just splicing into your main power wire that feeds the switchpanel, because it’s probably undersized to power the amp as well as rest of the electronics. Check to see what size it is, and compare to this table: If it’s 8 AWG you might be ok, depending on what else you’re running.
http://www.powerstream.com/Wire_Size.htm
How bad is it to fish a new wire? You could always snip out the existing power, tape the new, fatter wire to it, and use the old wire to pull thr new one thru the underbelly, then split off power (via buss bar, etc) from the new big wires into all the electronics including the switchpanel and amp.
Also, to be safe you probably want to put some kind of fuse on the amp wire, as close to the battery or perko switch as possible.
And remember, if you run a dedicated positive to the amp, run a dedicated ground as well. Otherwise you’ll overburden you ground wiring, which can cause a whole slew of problems.
PITA, right? Good luck, let me know if I can help out any…
Baker
Old, beat up 17’ McKee