When you use multi-channel DVD-Audio, do you keep inserted or not the SURROUND mode in the DSP Audio menu?

I notice some differences when you switch on/off the surround option, while I expect that when you are hearing at native, discrete multi-channel music that option should be useless/disabled (as in my Rotel pre-processor at home) and the amplifier should 'directly direct' the multi-channel sound to the respective speakers (maybe with the little difference that DVD-A are encoded in 5.1 and the ML enables 7.1 with its ten channel ampli).

Bottom line: I'd like to be sure NOT to introduce surround artifacts in original multi-channel music. But I even wouldn't like to force mchannel music to stereo mode...

Any ideas? Thanks!