I can't comment on the Oppo, but my main recommendation for the Denon 2900 is if you are looking for a good DVD-A/SACD player. The invisible layer change is nice but I've had a lot of reliability issues with my Denon and have only owned it for about a year. The main problem (with my unit, anyway) is that it randomly chooses to not play discs. You put in a DVD, the machine spins for awhile and then says "no play." Usually if you eject the disc and try again it will work but sometimes it takes several tries. There's no reason a DVD player that once cost $999 should have that much difficulty initializing. Also, it is very picky with discs that are only a little bit scratched. My LG DVD/VCR recorder always works as a backup, but this can also be pretty annoying. Thirdly, I've had a random problem with the color shifting; it seems to be a loose connection with one of the component video outputs on the Denon and can usually be fixed by giving the cable a little jiggle. Honestly though I haven't tested the cable to verify if the problem lies with the cable or the Denon.
Around Christmas time all these problems seemed to be happening a lot so I was starting to look around for a new player and considered the Oppo as a cheap alternative, as well as the Denon 1920/30 or even the recently reduced-price 3910, but I'm concerned about reliability. If I'm going to spend $600 on a DVD player I want the darn thing to last me more than a year. As it was the 2900 was fairly expensive and in some ways has been a disappointment, although I am living with it for now and do like it a lot when it's working properly.