You are describing the exact problem that I see on my 810 beta install, upgraded to RC.
Whatever orbiter I use, selecting audio or video gives a very very long delay, and SOMETIMES goes into what looks like a neverending reload, every orbiter, every MD, with the only cure being a reboot of the core via SSH. I have to turn the MDs off manually, so they aren't shutting down either. Which reminds me, I noticed SSH was slow as well, so maybe this is all down to network slowness once the problems have started.
I am going to do a complete wipe soon and start over with 810 final, and hopefully I won't see this issues again. Sorry Bulek, I realise that doesn't help you very much, but thought I'd share.