They will make custom set ups of their EQ products for you if you call them first and order it through a dealer. The SPC adds a little hiss to your sound when it is on but that is due to the mid range boost it is adding. When you are done using it just turn it off and the additional hiss goes away. 1 point knocked off for the hiss, although most frequency boost products suffer from this as well and you really don't notice it much when you are playing a solo. I use this when soloing and it adds infinite sustain through the 5150.
Chords sound fatter and rounder and sustain longer.
I can get my amp to feedback right away. Not like I used my bridge tone anyway. I've been playing for about 6 years. My whole setup is my Les Paul into a Bad Horsie, a Boss Chorus Ensemble, to the high gain input on the 5150, then a 482 BBE sonic maximizer, then a Boss DD-3 delay. It's loud thru distortion.