Bruno, I have DPLII(x), Neo: 6 and Neural Surround ambience processing modes available. I briefly experimented with them following Eric's(EFalardeau's)description of his more extensive tests some time ago. Although I did notice differences similar to what he described, I thought they were relatively small and I generally keep DPLII on without bothering to change according to the source material.
When you use them without surround speakers, just the center, the effect is relatively minor, since the only difference is that it sends part of the sound which is equal in strength in the left and right channels to the center channel. The amount is variable(by Center Width in DPLII Music or Center Image in Neo:6 Music)and at one extreme all of the material is kept in the main channels and then of course it sounds exactly like the regular stereo mode, with the center being "phantom".
The main purpose of these modes is to send reflected ambience(which is the majority of the sound reaching us in the concert hall)extracted from the front channels in 2-channel material(there was no place else to put it)to the surrounds where it belongs, making home listening a little more realistic. So yes, once you get your surrounds you should enjoy the effect of these modes more.
