no, rather you should do as I suggested and check the INFORMATION menu to confirm what is actually happening.
again, it's IMPOSSIBLE to decode a 5.1 signal and output it as 7.1 without SOME sort of processing taking place. Those extra two channels cannot appear out of thin air.
if you want to take photos post a photo of the front panel display (5.1 in > 7.1 out) as well as what's reported in the AUDIO INPUT SIGNAL section of the INFORMATION menu in the GUI.
if the unit is on and getting a signal it's doing some sort of processing...yes, the info shows just as you said 3/2/.1 but it DOES NOT use PLIIX to output 7.2
Well, to fair I didn't say you had to use PLIIx, just that the receiver must be doing SOMETHING to extract/decode 5.1 and output as 7.1.
I just checked the manuals and if you compare the "Surround Back" parameter options (pg 99 of the 3312 manual versus pg 74 of the 3311 manual) it does appear there is something new. The 3312 manual lists a setting called "ON" (typical Denon, very descriptive! ) which can only be used with a DTS signal and is described as such: "Convert the 5.1-channel source of the DTS/DTS-HD input signals to the 7.1-channel output recommended by DTS".
So an apology is owed as I guess *something* has changed. They don't really give any details about what actually is happening to process these two extra channels. Have you compared this mode (DTS-MSTR + SB ON) to DTS-MSTR + PLIIx? Does it actually sound any better/different? Also does it work with any DTS-MSTR 5.1 track?