My 600 also suffer from numerous problems. It doesn't recognise the Oppo on HDMI until I switch to another input and then back again, when turning it on. It outputs garbage to the screen so that I have to switch the screen off and on again for a new handshake and then it syncs ok. It's annoying, doesn't detract from the outstanding performance, but really seriously needs looking at in firmware.
HDMI has too much control over products. There should not be any need for me to even have my screen connected to the amp in order to listen to an SACD over HDMI, but the AVR600 won't play the audio unless you switch the screen on. Why? I have no idea at all.
There are serious failings with this machine's usability. Oppo have updated their firmware several times to fix issues and this is in stark contrast to other companies like Pioneer who took six months to release a DTS MA decode capability to their players. Arcam appear to be taking the Pioneer route.
At the very least they should keep their customers informed of firmware progress and which issues they're working at resolving.
And, yes, I've been in touch with them. Very helpful in terms of contacting me back, but no firmware updates as of yet. Come on Arcam!