I believe so - haven't turned off my surround backs to see for sure, but I'm basing it on the nature of PLII/PLIIx.

NEO6 was originally intended solely for two-channel sources, not as an extension to DTS. I'm not even sure if it can be used for anything except analog or PCM stereo inputs (it couldn't be with the original NEO6 decoding included in the Model 950). If you had surround back channels and wanted to get signals to them with a DTS track, you wouldn't use NEO6 to do it - you'd use DTS ES for that (similar to Dolby EX). If you were to have surround backs or if you had a DTS stereo source (which I've never encountered, although they may exist), you could actually use PLII/PLIIx to fill things out - it is capable of being used with both DTS and Dolby (and analog, and PCM).