last question... wat does this mean

-requires 10-gauge power and ground leads — wiring and hardware not included with amplifier -

 

That's talking about the power leads. You need one that runs from the battery all the way to the trunk, and one that just grounds the amp to the trunk. 10 ga is pretty small, I would use at least 8. If you are interested in that other amp, I prob can throw in this stuff for free.

To answer your other question:

car off = 12.5v
car on = 14.4v

I used the 4122 on a single 10" and it was ok. Not pounding but def added a nice bottom end. I don't really think it's enough for two subs tho.