Onkyo Video upconversion

I am getting lost & confused in the marketing speak & specs & ...
If anyone is familiar with these products, please help.

My setup: Onkyo TX-SR605 receiver & DV-SP405 DVD player, Samsung LN-T3253H(720p) & Cox Cable SA 8300HD. I have the HDMI from receiver to display & from DVD to receiver. Tried both HDMI & RGB from cable box to receiver. Oh, and I have a HQV Benchmark DVD on the way to help me, but in the interim...

The info I can find on the receiver states that it up converts all analog signals for single cable HDMI output & passes HDMI inputs up to 1080p. I can find no settings or display on the unit that tells me what the output rez is. The DVD tells me when it is turned on & if I hit the display button.

Here is my query: The RGB is analog, correct? So given the info above the SD cable using RGB should be cleaner than if I used the HDMI? I am getting mixed results from the cable. Some HD channels look no better than the SD channels & some of the HD channels look far better than other HD! Does this mean that the receiver is doing its job? Then why are some HD channels so crappy looking? I can notice a difference between HD & SD when I hook the cable directly to the T.V. via HDMI.

The DVD up converts & outputs 1080p as well, I have it set at 720p so as to minimize conversion, as it passes strait thru the receiver. If I use the RGB from the DVD then the receiver should up convert, right? The DVD looks good as I have it setup, I was going to see if the receiver does better or worse by switching to RGB.

I also had a grey bar oscillating up the T.V with the RGB from cable, rerouted the RGB cable away from everything & it helped. I am guessing that there was interference from the rat’s nest of cables & power cords, sound plausible?

I guess my concern is I want to be sure I am getting the best picture I can. I have 20 days left to return if it is not up to par.

Thanks.