COX Tech says 6412 can't record HD properly

So I've been having a ton of problems with my 6412 and Toshiba 52HM84 DLP set. Everything from full-blown pixelation and audio dropouts that prevent watching TV to an overall "grainy" look and feel to the picture. Often when watching HD anything with motion will go "out of focus" for lack of a better term and as soon as the motion stops, the picture snaps back in. As long as it's a still image, every thing is fine. Plus, I was getting a ton of subscription bug errors and zero length recordings. So after swapping out 2 boxes, and many many pointless calls to tech support, we finally had somebody come out, one of their "HD specialists". That turned out to be a joke. Tech comes out, I explain the problem to him. As i'm showing him some recorded shows showing the pixelation, he proceeds to unplug the cable to test the strength. While doing this, he looks from around the back of the TV and says "Whoa, how are you still watching TV, I unplugged the cable!" I told him it was a recorded show on the DVR, and he says "kinda like a VCR tape, right?" Yeah, exactly like that. He then looks at the back and asks me how I have it hooked up, he doesn't see any "red, blue, green cables" going to the TV. I told him I'm using DVI-HDMI, and he asked me what that was and if it's something new. At this point, I'm trying to figure out what the hell he's doing working for a cable company. Anywho, he tells me signal strength is fine, so no problem. I tell him that's fine, but explain the pixelation, grainyness, etc.. He said that the problem is that the 6412 box can't record HD properly, and that's why I'm having the picture problems. He said if I don't record anything, and watch it live, I'll be fine. I honestly was too dumbstruck to respond to that suggestion(why have the DVR in the first place if you can't record anything on it) so I thanked him and sent him on his way. While I'm drafting a letter to Cox expressing my disappointment in their customer service, anybody got any ideas on the poor picture issue? SNR looks good on both tuners in the menu, so if it's not a signal strength problem, what could it be?