I put the amp in the hidden storage compartment between the tracks. I just made a small slice in the "tray" to let the wires through. There's tons of room in there and I doubt I'll ever use it for much else. You need to get under that tray anyway to do the other wiring, so it's the easiest place to put it. I figure it's nice to be able to access the amp easily to adjust the gain and crossover controls. There's also a lot of room under the factory amp, but I wanted to maximize the air space for the sub.
I'm sure you could get Technic's harness. I paid him by Payal and he shipped the set to me. Alternatively it wouldn't be that hard to tap into the wires. You'd only need to to tap four wires for signal (they go to the under-seat subs) and they're pretty easily identified because they're thicker than the other ones that go to the regular speakers. Then you need to tap a fifth wire for the amp turn on (you have to do this regardless of having the harness or not). That's on the passenger side and is a thicker red wire with a grey stripe. All of the wires you need to tap into can be accessed from under the rear seat cushion (the part your butt rests on
), which comes out really easily - just pull upwards from the front and the whole bench will pop out.
Tehcnic's kit came with an
Audiocontrol LC2i which converts the speaker-level signals to typical aftermarket levels to feed the amp. You could just buy that item. The HK amp sends pretty high voltages to the sub so you need an active converter like the LC2i, I'm told the cheapie passive ones won't do.
You'd have to look at the harness that connects to the factory amp (which is where my sub is now) to identify the wire colors though. I'm using the technic harness, so I've never needed to map them. Since my sub is now sitting there it's harder for me to look at it without removing it.
Here's a picture of my sub amp (Alpine PDX 1000.1), and you can see where I attached the power wire to the battery (there's a bolt under that cover). To get to the other wiring to show you, I'd have to pull out that whole "tray". The tray is a flexible plastic so it's forgiving of having extra wire bundles routed around near it. My LC2i is by the factory amp behind the sub. I would have put that near the amp, but the included wiring connections from Technic aren't long enough, and the LC2i is very small, it was easier to to just tuck it back there.
If you're at all comfortable doing car audio installs you'll likely find this is one of the easiest you've ever worked on.