Sure seems there's quite a bit of voodoo here.
Uh, DVI is ONLY video, so as soon as you go HDMI to DVI, audio is gone.
Pepar you are close, HDMI is a 2 way protocol. From the source, it queries the next device to see if it has any multi-channel decoding equipment. If not, it will only send PCM audio down that HDMI line. The emphasis is next device, not some device a few connections farther. Nothing is "broken" it apparently works as documented. Which is not to say it's impossible to change, but I highly doubt they'd ever change this, their focus seems to be on an ability to pass some nice buzz words down the line (TrueColor, TrueAudio). You know, the kind of stuff you need test equipment to tell is actually happening (that was very editorial, BTW!)
Passport (or SARA or MDN) have nothing to do with multi-channel audio or in preventing it. What IS true is that there was a recent "change." WITH the current 2.5.066, when one chooses Dolby Digital as the preferred output port, the 8300 will actually shut off audio through the HDMI port. HOWEVER, if one DOES select HDMI, audio will still flow out the optical/co-ax port. Prior, it didn't matter what one chose for the output port, all things were possible. I actually prefer it this way, it's slightly less work for me late at night when I want to ditch my AVR for just the TV speakers. Now I can leave HDMI audio enabled ON THE TV and get nothing as my 8300 is set for Dolby Digital. I shut off my AVR and change the 8300 to HDMI and bingo, PCM audio through the TV speakers. With the older software on the 8300, I also had to turn TV speakers on and off.
Of course, the last paragraph speaks to a TWC system; as we know, with the same software, rev, and 8300 STB, things CAN be different in different cable systems. So it MAY be that what does or doesn't get turned on or off at the 8300 could be different even with the same software running on it!