You're on the right track here!!
I'm running 2 of the SPG-555 in my 07 Avalanche. Each one has a dedicated PDX-1000 and the rest of the components(BA Pros) running on a PDX-4.150. The subs hit hard and everything is sonically correct. The amps get very hot, which is a concern, and they suck a LOT of power. I'm running 2 yellow tops with an isolator and I still have problems with lights dimming.
2SS/RS, VR, Blk hockeys, Blk leather, MN6, sunroof, GFX
Delivered: 29 June 09 !!!
'57 BelAir 2Dr Post
'07 Avalanche LTZ (daily driver)
'10 Traverse (wife's demo)
'99 Harley FLHTC