Jeff is right…
Other solutions allow for Inout and output of signal in PPro.
The Matrox products are the only real solution for genuinely enhancing creative performance during the editing session. They do this by leveraging a combination of their own chips plus those of a paired qualified graphics display adapter.
However, you do find yourself at the crux of an interesting point in PPro history. Adobe has been showing it’s forthcoming “Mercury Playback” Engine. This is Adobe’s implementation of leveraging graphics hardware to do more in real time in PPro. I would guess it would be in PPro CS5, as they’ve been talking about it and demonstrating it. This has not been formally announced, however.
This means that because your workflow is essentially filed based (.m2t) there is no need for signal capture and output. If the Mercury playback engine uses the graphics hardware for acceleration one of the chief advantages of the current Matrox line gets reduced. I love Axio and RT.X2. compared to the long render times of the FCP suite I currently find myself in, I miss them a lot. But keep an eye on where things are going and spend your money wisely.
Hope that helps,
Alex