Definitely go with the proper car PC mate,
I brought my case and screen from MO CO SO all the way from america (i live in UK). Ive got the M4 ATX PSU. Definitely Recommend it!
I run the on board sound and seems to be okay? I have never got round to Sound blaster X-FI which I will be buying soon...
I use centrafuse on the free licence and have 15 days on that. Once this is up ill be going over to Road Runner
Up to you though as its your kit