How did this setup end up working for you?
I have something similar, except Alpine PDX amps for power, Knukonceptz wiring and a Pioneer P6900UB head unit for USB hard drive support.
I have everything hooked up except the SR124 sub. Haven't decided what to do for a box. Don't have time to build one...
I was also considering a Fisher box; you went with 1.20 huh? The SR-series guru over on the Polk forums suggested I go with 1.25 as the absolute optimal size. How does your SR124 sound in the 1.20? And how well is it blending with the SR-6500 comps? Coming from a 10" setup, I'm a little worried about the SR124 being quick and tight enough, so optimal box dimension should be crucial. How is the quality of the Fisher box?
I'm also trying to decide on the Alpine PDX-1.600 or 1.1000 to power the SR124...I think the 1.600 (around 750W@ 2ohms@14.4v) should be enough, but not sure.