A simple missed break in a switch statement, which allowed my vertex shader to bind to both the vertex and pixel stage was the issue. That cleared up the assert, and i'll be well on my way to multiple render targets shortly with any luck.
EDIT: the other issue was trying to render a cube with 8 verts, and 36 indices. Neither of these would have been a problem with my last my last stable version, as it would have identified the draw primitive error, and my shaders were not based on an interface. In order to get a cleaner interface that will be mostly compatible with directx11, I'm rewriting much of how my code handles DX9 objects, and there are still many bugs that need to be patched. regardless, I have the MRTS rendering, so now it's on to the second pass.