On the "front end" there are two SAT & two OTA tuners. I've looked through the cover. With the right control [14V, 20V, 22kHz] more than one transponder can send signals down the same cable to two tuners [SAT].
It seems clear that there is some logic behind how these "tuners" work that isn't readily apparent. I hope someone who knows something about how this box works under the hood will chime in. Are there four discreet tuners in this thing? Two SAT, and two OTA? I think it's now clear that, at least, the SAT tuners are not hardwired to the SAT inputs. Would it make more sense to me look at it like there are two MPEG2/MPEG4 decoders capable of getting their input from any of the 4 available tuners/inputs?
At one level it is capable of writing two bit-streams to the disk at one time. It can write one from OTA and one from SAT, or of course, two from SAT. Apparently, if the SAT channels are properly "aligned" in is capable of doing it over a single input.
The "back end" is for others that know a whole bunch more than I do.
Anybody want to chime in here?