Indeed. The psx lacks the z buffer which allows the system to render the polys in their exact position in the game's virtual space. The plugins can't read that z buffer because it doesn't exist.
Get the soruce of the game, modify it and reprogram it, then burn it and voila¡¡¡¡
well, it's actually do to the PSX's lack of sub-pixel accuracy. meaning, it only moves textures from one pixel to the other, not in between. at 320x240, its not too big of a deal. but when you blow that up 2 or 3 times, the distance is quite large, thus the shaky textures as it moves "only" a pixel or two in rapid succession