I'd investigate the GK 2001 RPB (
http://www.basscentral.com/2003/gk.shtml has it listed at $429, with a "call for price" so I'll use $429 in this post).
Rack mount preamp version of the 2001. Then get a real price/watt ratio out of a pair of Behringer Europower 1500's.. (
http://www.americanmusical.com $299.97ea)
Should come in about $1229 (the full 2001RB is around 1299 right?) for 2x900watts @ 8ohms, 6U rack, and preamp (less than $1029 if you forego the rack/make your own). Never run out of juice and always have a backup...
You could get into that preamp with 1 EP1500 instead of 2 for around $729... If you use a 4ohm cab, you'd have 1400watts with the EP1500 for almost half the price...
Granted you'll have a 80lb+ 6U rack with those two EP1500... but

2x1400watts at a cheaper price point than 1x1050watts
Personally I'd do it up as 2x2U racks for power and 1x4U rack for preamp, EQ, power conditioner, etc.. Stack it all up then cinch it down to the top of the cabinet with a couple of load straps. Cause it will vibrate off. But I'd start with 1 EP1500 and preamp to see how I like it.
If I hated it, at least I'd have a power amp that could easily drive my cab. Bonus to that is any amp/preamp with a line out can now drive that cabinet too...
Sorry, I just can't get away from being modular... Its so much more cost effective.
oh I just reread.. you already have a GK preamp/amp, so for 300$ you're all set with enough power for your aggie. With a little extra for a 1x15 or 2x10 cab straight out of the GK
