is there something wrong with the 8 cubes you have now? 6.0 per driver is MAX what I'd do.....but think, you have a 1000.1 powering two 15's.....imagine a 1000.1 PER driver, or a 2500.1........
Met Scottie (which i have known for years) at CES, man he got us all excited here at work about XS Power. Looks like XS has some new, exciting stuff coming down the pike, ought to be a great 2010.
final impedance will be 1 ohm, so here are just a few.
http://www.sonicelectronix.com/item_17598_...+BXi+1610D.html
http://www.sonicelectronix.com/item_6190_P...ik+A2400DB.html
http://www.sonicelectronix.com/item_17654_...+BXi+2010D.html
http://www.sonicelectronix.com/item_17555_...9+Edition-.html
http://www.sonicelectronix.com/item_17599_...+BXi+2610D.html