It will keep you from having to spend money on a new amp sooner than you might have to, that's for sure.....if he ran all 3 you are probably going to need a new box for 2....give us the model # for the subs and then we can help you get the most bang for your buck with that too.......

 

they are alpine sws-1234D ... i think. hmmm DVC ... 12" ... type s. haha

 

When you're looking to replace that amp, find a nice mono block that will deliver 1200 WRMS into a 2 ohm load, and use all 3 subs like your drawing up top (and then you could also add a fourth sub like it with no problem). And then use your MRV 757 to run a good set of component speakers up front.

 

im thinking about buying a second amp ... an alpine MRP-F356 to run some more stuff off ... perhaps the third sub on its own, as well as some 6x9s ... is this do-able? if so, how would i wire that up?

 

Buying that 5 channel amp would be a waste of money for you.....no matter how you wire it up, the power delivered to either fronts, rears or subs will be out of balance somehow......

Using the 757 to run your fronts will leave you with 30 or 40w X 2 for your rears and around 150w to run 2 of your subs.....if you can find a decent quality mono amp that will do around 5-600w @ 2ohms you can wire all 3 of your subs for a 2.67ohm load and run the rears off deck power for now. If your budget allows there are obviously more options but this would be a good next step.

The trick to saving money on this stuff in the long run is to get equipment that works in your system now and can be used for another purpose in an upgrade......

HTH