nVidia originally said that the 680i boards would support Yorkfield CPU's. This was based on preproduction samples. Then nVidia and Intel got into a p*ssing contest, and when production CPU's arrived, the 680i chipsets did not support Yorkfield. I do not know where the 630i's come in, but I suspect that's true for them also.
Your experience seems to bear that out. You might try to update the BIOS with your old chip, then try the Q8300 again.