System check

I have not had great experience running MTX amps at less than the loads recommended (in your case 1.5 ohms would be under their 2 ohms recommendation), but they are solid performers otherwise. I'd say no to the MTX because it doesn't meet your system needs.

I also would probably not recommend th Sony because it is not a solid performer. It probably wouldn't run your subs very cleanly althought they may poud well. They aren't known for running cool either (it'll run pretty hot with the load your proposing).

I don't know what advice to give you for powering your subs (a 1.5 ohm load?) but I do know that those two amps probably won't suit your needs. (You need a 1 ohm stable amp if you don't want your new investment to go up in smoke, literaly)

One more thing. You are honestly doing way more harm to your system by putting your speakers in a  generic box as opposed to a box made to spec for your subs (Hopefully you can find a prefabricated box very close to the spec needed for your subs to perform well). If you put them in a box that is not suited for them it won't matter what amp is running them they won't sound good.

                                                                                             Colin a.k.a. bLaZ