Many of the suggestions in that thread (seem to) apply to SARA software based units, not Passport Echo, which seems to be what *most* TW divisions use.
That said, there are some compatibility issues between the boxes HDMI output and some TVs, especially projectors. The most widely used s/w release in use, v1.8.103, has these but the next release coming (it's been approved by TW corporate engineering and already deployed in some areas), v1.8.112, has resolved a LOT of these.
One thing to be sure and do is 1) turn the TV on first and wait a few seconds, say 5, then 2) turn the 8300 on. The two will NOT handshake properly if the set-top is turned on first.