I think i may disagree with this answer. I believe dxm had activity at the kappa opiod site <in addition to ndma antagonism of course > and I think suboxone is one of, if not, the most potent kappa opiod antagonists out there. I've done dxm for years. I used to love to do it on methadone, and doing heroin at the tail end of a good dxm trip night possibly be the best feeling ever... but taking it with suboxone it definitely is different. I can't put my finger on what it is, but I do actually think it loses some of the psychedelic effect. Note this could also be due to enzyme interaction.
To the poster above me, no offense but when looking at stuff like this you have to consider everything not just receptors but also activity of enzymes especially with dxm as it effects the dxm to dxo ratio which is basically yep different drugs in the body.