Mac guy wished to discuss PC audio settings, [accept] or [deny]?
[Accept]
Hey Rackoon
You will get much better sound quality using the EQ, amp and car speaker setup but, you'll have to use the on-board sound cards output as your pre-amp to feed the later stages.
I'd recommend you keep the PC's output volume low, like 30%, and let the big amp do the real work. Using the EQ you could then filter out some of the hiss and really crank up the BOOM! I run a subwoofer setup on my first cab, the only one that is playable so far, and it ROCKS! I also use it as a juke box for while I'm working and it's great. If you like jammin good tunes while you work, you'll thank yourself for the extra effort.