First off, that's not a ridiculous sub.. they're $20-70 subs at best... not a ridiculous amp either but just letting you know what you have to work with.
Secondly, you're going to need to do the following if you want a quick way to wire this to the FRS:
1. Run a wiring kit from your battery to the trunk (suggested 4 gauge wire and quality fuse). My amp came with signal sensing so I didn't run a remote wire but ymmv.
2. Buy a Line Out Converter (PAC brand w/ RCA outs will be fine)
3.
USING THIS THREAD AS A GUIDE, Splice into the rear harness via the Speaker inputs from HU (3. 9. 4. 10) and using taps and wire the Line Out converter to them
4. Hook your amp and sub up as per usual
5. Enjoy
For extra points you can use Google to search the forum for all these answers very quickly using the link in my sig (How to Search)