I used the RME400 on Leopard without problem. So for me, (sorry if I'm stating the obvious) the conflict is clearly between the RME400 driver and Snow Leopard, or something in Snow Leopard. Like some users, I had periods where things appeared to work fine, then not.
After too many crashes and problems, I had my Mac Pro checked by an authorized Mac dealer, and upon its return to me, it was fine for a few days, then started acting up again. I eventually removed all traces of the RME400 driver last week, but then still had problems - no freezes, but applications were hanging and taking longer than they should, then one of my 4 drives inexplicably failed. So my Mac is now back with the mac dealer.
Prior to that I had given apple the information they asked for concerning the RME problem.
My reason for saying this is that the ongoing kernel panics, crashes and freezes are eventually going to cause additional problems to the computer hard drives, so that there are then numerous problems, not just the root cause, thus making whatever is causing the conflict to begin with even harder to identify. I don't know if this is something that all users experiencing problems with the RME drivers have considered? I've spent a lot of my time trying to fathom this problem and I believe that the issues my computer have had were triggered by the RME drivers in the new OS of Snow Leopard, but I don't think it's right to apportion blame on RME.
As a pro user, I find all this frustrating beyond belief. I've lost time and money over it and I want to use RME400, not anyone else's audio interface. From what I know of the complexities of Snow Leopard and from what I've seen on this forum, it appears that RME are trying to resolve what is a very complex and opaque problem brought about by the new Apple OS. However, with apple now involved, hopefully a solution will be forthcoming, sooner rather than later.
Mac Pro 2 x 2.8 Quad 32GB Ram
All that we see or seem, is but a dream within a dream.