I've followed the install guide and got widescreen and the crisp filter working on a widescreen compatible game (DQV), but I've not been able to get screen filters working in non-widescreen games. Any idea?
Depends on what patches you're using.
GPU scaling is strictly linear upscaling, as it's done only by the GPU, and it doesn't really support anything else.
Scale matrixes only work with the built-in capture card.
However, due to the mathematical complexity of the upscale matrixes, I opted to disable scaling for the X axis in widescreen mode, and only let it to be applied to the Y axis (you can see if you look really close, that changing the matrixes does indeed somewhat change how the overall image looks).
Technically there is only mathematics stopping me from making the upscale matrixes widescreen-compatible. Some could be probably "just upscaled", but the others must be recreated from scratch due to their complexity.
The only downside to supporting widescreen upscaling matrix is that pixel perfect mode (START/SELECT on boot) might be garbled, and/or hang, unless I patch out some unrelated functions.