Results will be nearly the same. You'd be running a 4 ohm bridge on the 4 channel, the amp "sees" 2 ohms. The mono amp would be wired at 2 ohm as well. 4 channel would have less distortion and be a little better overall for SQ, but the difference is negligible and in all honesty you usually won't notice a difference to a certain point. The 4 channel would draw more current to deliver the same amount of power that the AB amp would.
So the mono amp would be better for 2 subs since it'd be more efficient rite? What kinda specs should i look for in a mono amp to run 2 subs? Should it be stable to 2 ohms? Thanks Jonathan.
There will be a difference if the amps are different classes. Some manufacturers make mono amps that are class AB, such as audiobahn. 4 channel amps are usually class AB, but if you get a mono class AB amp, there'll really be no difference. If you have a weaker alternator, then mos def get a class D amp. Otherwise, I doubt you'll notice any difference.
Go for a mono amp for 2 subs as you'll want them both playing in perfect synchronisation, a 4channel amp for 2 seperate subs can sometimes cause the bass alignment to go out meaning less tight controlled bass. Also efficiency is important unless you've got a big power cap. The class AB will have less distortion than the class D but most distortion in the big mono amps has been set to only effect the higher frequencies and your low pass filter will take care of that.
Cutty, you should look for mono amps that are at least 2ohms stable, 1ohm even better. For power, add up your 2 subs and find amps that's close to that, if not slightly greater. Also, look for amps with built in crossovers. Makes it easier to tailor your sounds. Do stay away from Pyramid, Sony, Pyle, Lanzar and few other no name brands. They do not tell the truth about their amp's specs.