For that price on the box (140?) you could have gotten one built to custom specs locally.
You don't have a 4 channel amp to run your speakers and the Boss won't put out as much as the current HU....
Personally think you over paid for the 12 (SA-12 will do what you want) then again that's your choice.
if you didn't order it all yet id change a few things if not play with what ya got. Just know once you open the box its used and the value drops.