I can’t speak directly to your problem, but I would suspect something on the software end. If the hardware were having a problem, I would expect it to be much more dramatic (buttons not working at all, or cutting in and out). A delay in the software processing a command sounds like a setting in the software, or a driver issue.
That said, make sure you have the most up to date firmware on the Denon. There were a few minor glitches in the system when it was first launched that have been ironed out with firmware updates.
I’ve been using my 6000 since it was released in North America, and it’s a good, solid unit. Love it. Mind you, it’s also a totally different kind of beast than the NS7 – if you are looking for a scratch workflow with moving platters, well, the 6000 certainly isn’t your answer.