With a 5.1 setup using a 7.1 receiver, you will get PL II, but not IIx(this is the 6/7.1 version), DTS but not ES, DD but not DD-EX, and I'm not sure if DTS NEO:6 has a 7.1 version, but you would not have that either.
I'm running a 7.1 Denon with only 5.1 and the receiver simply omits the modes it cannot produce based on speaker configuration.
Ed
* Sierra-2EX's W/V2 crossover upgrade
* (2) Rythmik F12's
* Parasound Halo P6
* Audio by Van Alstine DVA-M225 Monoblock Amps
* MiniDSP 2x4HD For Sub calibration
*World's Best Cables Canare 4S11 speaker cables