Make sure the 622 DVR doesn't have a volume control that's turned down. My dad had that problem with his cable box recently - he was having to turn the TV all the way up because the cable box's volume was turned down to about 50%.

I don't know about the 335. As I recall, the 990 doesn't have a way to report the input signal's format, but you can tell a lot from what the active surround mode is and what modes are available. You will have some channels in Dolby Digital, in fact I wouldn't be surprised if most or all of them are that way, but you'll only get 5.1 from HD channels and that will depend on the specific programs you are watching (some will be in 2.0 and some in 5.1).