I agree with bill on all points, and just want to add, you have two choice... whole house audio (sonos would be a good fit for this. ) or a 2 zone receiver, anything will do as long as it has a zone 2 preamp out. an amplifier that can handle all your speakers.. and, here is the big x factor...
http://www.overclock.net/attachments/sound-cards-computer-audio/158916d1275877478-answered-sound-card-logitech-x-540-maybe.png That's all i could find that had anything to do with the model you have there.... never seen or installed it before. hope it helps, good luck to you.
Always a fan of Denon AVR-2311ci -620 They match well with almost anything, partial to Paradigm Ref Studio 60's - 1100 a pair, Paradigm CC-490 (center channel) - 475, Paradigm ADP-390 -450, Sunfire HRS-10 -600 thats what i would do with your money.
Partially correct, the room size (height, width, and length) and distance from sub matter. Think about it. If you stand right in front of a sub and slowly walk around the room, you will hear a difference. on the other hand, if you sit down and listen to your sub, then go move it over 2 feet and...
another thought, save a little more money and get yourself a respectable home theater in a box. something like a paradigm cinema 70 (about the $500 range) or cinema 90 (about $700). this would get you the full, entry level, 5.1 set up all you need is a receiver and wiring. then slowly upgrade...