I'll give you folk the rundown here first.......

So I just bought a Crate 1200H half stack:

GT1200H 120W RMS Head 4 ohms
GT412SL 4x12 (100w each) 8 ohms

And obviously I'm only getting about half my power out of the head due to the fact that the impedance of my cab is 8 ohms and my head is 4 ohms. So the natural decision for me was to add another 8 ohm cabinet, run it in stereo with my original cabinet, and bring down my impedance to match my 4 ohm head, thus getting full power. This makes sense so far right?

So I added:

Behringer Ultrastack BG412F 4x12 (100w each) 8 Ohm Stero 16ohm Mono

So logically, if I run my Crate 1200h head which is 4 ohms, into both of these cabs, which are 8 ohms each, I should be running at full power (objectively how loud SHOULD this sound? Like, in my living room or something I shouldnt be able to run it at full power without knocking stuff off the walls?).

Now my issue here is that I don't really know very much about this sort of stuff, and it seems to me that my Crate head only has one output. But both of my cabinets have dual input jacks (for stereo purposes I would imagine) so how do I run this all together? Do I split the original output with a Male2FemFem adapter and then split that again for each cab? Seems to me that thats the only way I can do it but I'm not really sure. Seems like an awful lot of splitting. How do I connect my 4 ohm head to two stereo dual input 8 ohm cabinets? Am I way off base on all of this?

Anyways, HELP!!!!!!!!