Whip, I've tried mostly DPLIIM and Neo:6M when listening to 2-channel music source material and decided that I had a slight preference for DPLII, so that's what I use now for all 2-channel sources.

As to the Denon "Matrix" mode, I don't use that, but my understanding is that it simply duplicates the front channels in the respective surrounds and also adds an adjustable amount of reverberation. Therefore, it doesn't make use of "real" surround ambience contained in the source material(in varying amounts)in the way that DPLII and Neo:6 do. I'd think that this would be a preferred mode only if the material contained almost no "natural" ambience. My experience has been that all classical material and even most pop items I've briefly experimented with benefit from DPLII.

Enjoy the music, not the equipment.