[soundman98]

first, i would not recommend using the oem amp wiring for that amp. definitely run your own new line off the battery to power it.

as far as that amp, i don't see any immediate documentation on jbl's site indicating it can be bridged, so it most likely can't. meaning that you could run a sub off it, but it will need to use only 1 channel, and won't get any more than 60w, which is pretty weak for a sub.

the 3 options are really,

use that amp, because i assume you've already got it, and let the chips fall where they lie.

get a different bridgeable 4-channel amp and run as you'd like in the first place.

get a 2 channel amp, and setup oversized power wiring with fused splitters and everything to eventually add the sub amp later.