Have you tried pushing the front panel buttons and then using the navigation pad to scroll up and down through the options? That's the way the 990's front panel works.

The Oppo 971H is not HDCP-compliant, so there shouldn't be any HDCP handshaking going on. It's odd that the player and the Model 970 would interact in such a way as to mess with each other's power commands. Has this behavior recurred?