I have always found Yamaha's interface and displays dealing with DTS-ES/DD EX confusing.
Scenario - RX-V2700, Play X Men Last Stand from my PS3, bitstream over HDMI selected
With the EX soundtrack selected, when you cycle through Ext Surr you get Off, Auto

LIIx move, PLIIx movie:On. Pick either of the last two and the display will show 'STRAIGHT/Dolby Digital'. The Dolby Digital and DD PLIIx lights will light up. Hit straight again which puts it into a mode where you can select the decoder, and the display will show 'DD D+PLIIxMovie'. The indicators stay the same. I believe both of those are saying the same thing.
Now I switch to the 6.1 DTS ES soundtrack on the same movie. I cycle through the Ext Surr options and I get Off, Auto:ES Disc, PLIIx Movie:On. Unlike DD EX, you get different results whether you use Auto or PLIIx.
With auto, you see 'STRAIGHT/DTS' with the DTS, discrete and ES indicators on. Hit Straight again and it show 'SUR. DECODE/DTS ES' with the same indicators. I believe this is saying the same thing. Confusing, to me
Selecting PLIIxMovie:On and you see' STRAIGHT/DTS' with the indicators DD PLIIx and DTS on. I am not really sure what that's telling me
If it's discrete, it must be decoding the 6th channel. But is it then using the DPLIIx decode to matrix to 7 channels? Now hit straight again, and it says 'SUR. DECODE/DTS+PLIIx Movie' with the DTS and DD PLIIx indicators on. I assume that means the same thing. Confusing, as I say
Some observations... Clearly X Men is properly flagged. Choosing Ext Sur Auto seems to be the correct thing to do, at least for this movie. It's odd how toggling Straight gives a different text readout, and confusing. But I don't believe hitting straight actually changes how it's operating, just how it displays the current mode. I believe DPLIIx includes the EX decoder as part of it's operation. But I don't fully understand what that means. Selecting PLIIxMovie:On for the DTS ES soundtrack does "something" I guess? But I don't know what. Is it decoding the discrete track? I would personally avoid that mode as I don't understand it.
I have a Yamaha RX-V657 in the bedroom, but no surround speakers on it, so I can't play around with it.