I didn't know which sub-forum I should post this in because it's about a home theater receiver.

I have both a Onkyo TX-NR515 and an Onkyo TX-NR626, which I bought for both the good upscaling capabilities but also because I needed a new receiver.
I'm just having some difficulty in deciding which one I should keep, cause I thought I'd sell the other one. Does anyone own either of these and could help me along the way? Is there any difference in the upscaling processors in them? is one better than the other?

Also, just as a receiver; which one do you prefer?

I dont know about these. Going by the higher model number, that one I would keep.

That was my initial thought as well, because it has 1 or 2 features that the lower model doesn't have, but I'm a bit worried because in a review I read they had problems with the subwoofer audio levels. Wanted to know if this is something that will be a hinder. Also, I was wondering if the Laserdisc community knows if the Marvell Qdeo video processor is better in the newer model than the older, or if they are the same.

Can’t tell about the subwoofer output. Marvell produced only one chip. That will be identical on both. There is more to it than the chipset. You will have to compare both and see. If I had to guess though I would say you won’t see a difference. Unless there is a bug, keep the highest model.