No need to run through a receiver if you have a good sound card or USB DAC.
Need? No. But if you're spending $250 on a sound card, why not just get a receiver which does the same thing but better?
I think maybe you misunderstood me. I ran the Klipsch ProMedia 5.1 Ultra's through a couple of different sound cards over the years. I was never unhappy with the sound quality and I never spent $250 on a Sound Card. But once HDMI became standard, I figured why bother with the sound card? I'm going to be using HDMI regardless and now I can use my speakers for my 360/PS3 as well rather than the TV's speakers.
However my point was, the OP is looking at $1,000 for just a pair of speakers. I'm assuming he's got higher standards in sound than I do. I can't say I've ever compared the sound quality of a $250 sound card to even a $250 receiver (say a Denon AVR-E300) but I can't imagine the Sound Card being any better (maybe that's a lack of imagination on my part). You get far more for your money with a receiver.
I snagged my receiver on a Woot special or something like that for like $300. 2 zones, 4k upconvert, like 5 HDMI inputs. Not to mention being able to use a remote to control my volume without using a 5 1/2 bay. Not saying you can't get good quality sound out of a sound card, it just seems like a waste.