Recommendations to get most from new Head

[ncbassman]

Hello everyone,

I have 'lurked' in the talk bass forums for a while and have really learned a lot from everyone. I recently upgraded my head to a Carvin BX1200. The amp is as follows (via the Carvin site):
- RMS 8 ohm 275W/ch, 4 ohm 400W/ch, 2ohm 600W/ch
- 8 ohms Bridge 800W, 4 ohms Bridge 1200W

I previously had a Ampeg B series amp that went down to 550W at 2 ohm. So I have 2 4 ohm cabinets:

Ampeg B-410HLF - 4x10 with horn, 400W RMS
Ampeg BX115 - 1x15 with horn, 300W RMS

Ideally, I'd like to have a 4 ohm configuration to get the 1200W bridged from my new head. I have read great things from the fearful designed 12/6 and an contemplating that. Maybe a 12/6 and a 15 sub, each at 8 ohm to get a 4 ohm total load. Or even a 2x12 cabinet.

My main question is the midbass/horn component. I know with horns, it does not effect the impedance, with the 6" driver (the Alpha 6A is 8ohm), does it NOT drop the impedance of the 12/6 cab to 4 ohm as it is set up on the crossover?

Sorry for the wall of text, I wanted to try to put as much info about my current setup as possible.