how good does the kicker L7'S sound ?

The L7, when given the amount of power it requires, will be a little bit louder than a comparable circular sub in the same situation. This is strictly due to the fact that a square covers more area than an equivalent circle, thus pushing more air. The difference is minor, & not noticable to the ear.

The L7's aren't very efficient (low dB rating), so they require more power (RMS watts) than similar subs to perform as well as they can. Basically, if you get an L7, you need to give it as much RMS power as it can handle, if not a good 50 watts more.

I couldn't find the amp you listed on Alpine's site, so please list the specs for this amp if you want to know what ohm subs to get, & how to wire them.