I have installed SSF last weekend and the upgrade is well worth it- especially considering it is just installing standard components with minimal configuration required.

Amps: I have the exact same amps. So far, no complaints.

Speakers: I considered the same speakers, but in the end I picked different ones Dayton Audio DAEX58FP, the main reason being the ones you selected use an adhesive to stick to the surface, and I'm not sure if that will last.

My motherboard supports 7.1 out of the box (green plug for 2.1 audio, blue plug front speakers, grey plug (PC case headphone plug) for back speakers. So I cannot comment on the external USB card- but I'm guessing that will do.

The sub is used for the game (ROM) audio, the mechanical noises don't need that much punch in the low frequencies. The bumpers make a nice sound and that impact noise is enough for me.