Cables: Radio Shack or Home Depot, or one of the other generic brands. You won't notice a difference. And even if you do, you won't break the bank and the difference won't be huge. See massive debates elsewhere on these forums. Also see some rather informative articles posted in said debates, the ones with all the graphs that make your eyes water and your mind ooze out your ears.
The subwoofer's crossover will override the rest of the crossovers, as it's the last item in the chain. This does not mean that it is the best item to use for the crossover. The best part would probably be the receiver (or integrated amp, but those usually don't have sub outs, at least not the stereo ones, so you'd have to fiddle with it.)
Anywho, if you can stretch your budget a bit, you might want to look at the H/K 325. It's where the features really start to kick in in that line, and you may be able to get it fairly cheaply as a refurb (from onecall).
I would not set the bass at the soundcard; all you really want that to do is send the digital signal to the receiver. (Mind you, I don't have a soundcard like taht, or a HTPC, or anything of the sort.) It just seems to me that your media player/reader should not be the thing handling how the music/movie is going to sound.
The analog cabling as you described it should be fine, but I would go with the digital, as I, personally, don't trust (or like) 1/8" jacks. They die too easily.
Anyway, good luck!
Ken
