amp/sub combination recommendations

I have a 91 mustang coupe. building a sub box in the trunk below the rear deck. Sub(s) will be firing down and have about 2.5 inches between and the floor of the trunk and the box. (its really the only way to keep trunk space, the spare and still fit subs in the car). I am currently using a JL Audio 6450e 6 channel amp. I have a memphis audio m1 12" 4ohm DVC running at 8 ohms because the amp is not stabe at 2 ohms bridged. I also have access to sony xm-1004gx and sony xm-1902gx instead of the JL amp. I have been researching, and i am thinking the JL amp is the way to go. At 4 ohms bridged with it produced 378 watts on the sub channel from what I have read.

First, would anyone recommend I use the Sony amps instead off the JL amp. I do also have the bass knob for the JL amp.

Second. Obvioiusly I am not taking full potential of the amp running at 8 ohms. I could rewire it to run each voice coil in stereo at the amp to the to get more power, but that would require me putting a hole in the box in a different location which I do not want to do. The box is a loaner... and it barely fits and takes up my whole trunk.

Since I have to build a box I want to try and get some more bass out of my trunk. I have a few options

Keep the M1 and wire it stereo to the amp. This should in theory double the amount of power the sub was seeing. I am OK with this but ive never really liked the idea of running my voice coils seperate.

Get a single/pair 10 inch subs that run 4 ohm

Get a single/pair 12 that run 4 ohms

The amp will be bridged for the sub channels. The 4 other channels will be running 4 ohm stereo pushing infinity reference components

I have limited space and 1.5 cubic feet is about all I am going to squeeze out of my trunk after speaker displacement. I am planning a sealed enclosure but am not against a vented enclosure if the speaker permits it in such a small space. I would like to pick up something that will sound good, efficiently handle the power my amp will put out, but not break the bank. I have been leaning towards a pair of 10's because of space limits. I do not care if the speakers are a mainstream brand... Give me some recommendations.. What would you recommend?

also, I wouldnt be opposed to something like 3 8's either.. I saw something on the net where a guy had 3 8's that sounded really nice

bump... still looking for an answer