It was a good buy, but you shouldn't have bought a single subwoofer, if it's the DVC 2-Ohm version. Right now, your wiring options are either to wire it down to 1 Ohm (makes your amp generate a ton of heat, and many amps aren't 1-Ohm stable), or to wire it to 4 Ohms, but both amps you list make less power at 4 Ohms. You'll still be fine with "only" 300W going to the subwoofer, it's not like you'll hear a difference, but it's something to be aware of, that you need to be looking at the 4 Ohm rating, not the 2 Ohm. This amp, for example, has almost perfect power for your situation:
Amazon.com: JBL GTO7001 Grand Touring 700-Watt Mono Subwoofer Amplifier: Car Electronics
Or, you can get something like this Kicker, which is 1 Ohm stable and will give you more power:
Kicker DX500.1 (10DX500.1) Mono Class D Car Amplifier
This JBL gives you an extra 50W at 4 Ohms:
JBL GTO-501EZ Monoblock GTO Series Class D Car Amplifier
Or look in our hot deals section, threads like these:
http://www.diymobileaudio.com/forum/hot-deals/130683-nvx-amps-similar-specs-ppi-phantom.html
http://www.diymobileaudio.com/forum/hot-deals/132973-polk-refurbs-amps-subs-speakers.html
Edit: I haven't researched to see which of these have line-level inputs, or the best way for you to go around getting the subwoofer to interface with your stereo. I do know that those newer Accords have wonky setups. A friend of mine got a system wherein he kept the factory head unit, but had to get a secondary volume adjust installed. The new Hondas change the EQ as you change the volume. They cut bass output so that you don't blow your speakers jamming down the street, so I recommend going to some Accord forums and doing some research. If you just try and splice line-level off of the rear speakers, you may get bass cut as you turn up the volume.
