Just saw this. Was having the same problem with my 520. Never narrowed it down to DTS. Will give it a try.
The problem made me think it was my DVD player. I changed that and went from coaxial digital to optical. That second DVD player was defective (not recognizing discs or recognizing them incorrectly) so I'm on my third. The current DVD player will accept either digital or optical so I'll give it a shot and get back to you.
By the way, I bought a 525 but it was mail-ordered and I believe it arrived damaged. Decided to keep the 520. There was a minor problem with the 525 that I've seen documented by others here: you lose a few seconds of sound at the beginning of a disc. I don't remember which mode of processing you are in (maybe all, if changing from one mode to another). Anyway, it was a non-lethal but annoying characteristic - and not related to the shipping. Does yours do this?
Other than that and the fact that the processor was apparently damaged in shipping (causing ear-splitting harshness in other than 2 channel audio), I thought the 525 was a definite step up from the 520. It was more powerful and the 2 channel audio was outstanding. I soured on upgrading by mailorder and the local cost difference is just too much to justify the upgrade.