I understand your modus operandi but I'd like to make a couple of points before you get on the phone with QVC 
In my experience a motherboard from a reputable manufacturer is going to be of higher quality and more compatible than a put-it-together company's products. Other than the motherboard, what difference is there really? And things that aren't compatible initially get fixed. That's because it's in the motherboard manufacturer's business interests to do so, less so for the system assembler.
I've fiddled around with online system configurators, but aside from steals on refurbs, most prebuilts are going to sell you on one or two things you don't need. If you have the knowledge to put a system together yourself, by all means profit from it.
