These sorts of issues generally are related to HDCP handshakes. You may want to look for a pattern in what order you are turning devices on - the cable box may want to be turned on after the TV and 990, so that both of those devices are on when the box tries to get its initial handshake. The 971H does not use HDCP, since it isn't a required part of the DVI spec, so there's no issue to be had there.