Just a little update in my situation. I tried the reflow bake method a couple of times with no success. I actually got back the network and firmware functionality, and was hopeful it might have worked, but alas, the speakers still did not work. So off to an authorized repair center I went.
Dropped it off and paid $50 to have a tech. diagnose it. Several days later talking to the tech., sure enough, it's the DSP processor that lies on the HDMI board, a common repair he's done several times on this model. Total cost for repair, plus the $50 I already gave them, is $420. Ouch! I said hold it a day or so while I decide to either have it fixed or buy a new amp (was leaning toward the latter).
I gave Onkyo a call to see if they could do anything, not expecting much. After explaining my problem, the support tech. at Onkyo said to email their parts division (parts at us.onkyo.com)., and they would get back to me hopefully within a week. So I shot off an email saying I have the same problem everyone else has had with this model, it's less than two years old, out of warranty as I bought it open box, yadda yadda. Again I didn't expect much. I even asked if I could buy they board and install it myself to save a little cash, knowing this was probably not an option.
Much to my surprise, I got an email back a day later saying they will give me an extended one-time warranty repair, and have it repaired at the service center I already dropped it off with! Sweet! I also asked if they have corrected the issue, and he said he thinks they are using a board with better capacitors in it to correct the problem going forward. Hopefully that's the case.
Anyways, when I thought that I was going to buy a new amp, even started to look at different brands, Onkyo pulled through for me. I hope to have it back sometime next week. So for anyone else also having this problem, it might behoove you to email their parts division and see if they'll help you out. Good luck!