A really long time ago I submitted two reports to Erowid detailing ayahuasca and salvia combos. Search for the author "nowhereman" if you want to see them. Salvia seems to potentiate oral DMT to an extraordinary degree. I don't typically get visuals when using just salvia, but after using it during a moderate-strength ayahuasca trip I could barely see through all the DMT visuals.
I experienced hyper-spatial perception (as in, more than 360 degrees of rotation) for the fist of just three times in my life with the combo, which is something that is typically associated with high smoked DMT doses, and even then only rarely. I was "rolling" through a hyper-spatial labyrinth populated by three-dimensional shadows--no elves or "smelves," though.
The second time I mixed ayahuasca, saliva, and smoked 5-MeO-DMT (on top of the salvia). At first the only thing present to my experience was a single strange symbol that resembled an "a." It divided into more copies of itself, at first to the right and left, then forwards and backwards, up and down, and then extra-dimensionally (though my sense of hyper-spatiality was not as strong as the first time). When I looked at the swarm of symbols that ultimately accumulated during the process I was overcome with the sense that I was looking at myself. It was incredible but extremely uncomfortable. My skin was tingling so much it burned. I fell over a few times on my way to the bathroom, where I puked. I think it might have been due to the combination of an MAOI and 5-MeO-DMT.
Both trips were substantially different than any of their component chemicals are alone. For instance, I always think I'm "leaving" with some type of group when I smoke salvia alone, and I get up an walk around, but with the combos this phenomenon was entirely absent.
I still plan to IV synthetic DMT and salvinorin-A at the same time. I'm struck by the compulsion less these days though.