Found the following, very interesting, today's date (Christmas Day!):
Perhaps someone more in the know can interpret in depth. My take is that something *is* being set to disable firewire on specific channels.
FWIW, in the diagnostic dialogue on my Motorola DCT6416 III, Channel 209 (CBUT High Def) D06|CCI is set to 0x02. Channel 3 (Regular CBUT) shows nothing for this same setting (blank).