DVD is normally at least somewhat quieter than CD (doubly so with most recent CD releases) and broadcast TV. This is intentional, as it helps provide more dynamics. A difference of 28dB seems excessive, though. For that matter, a +8dB setting is very high.

A few things come to mind. First, have you calibrated your 990 yet? If not, I'd recommend using the automatic or manual setup options (described in the manual) to get the 990 configured for your speakers and room. Also, I'd check to see what processing modes are in use for each input. Combining 5 Stereo or 7 Stereo with a CD could increase the difference between sources.