@Jofo well, being that I now have several versions of the PSX bus reader, I can talk about my results with all versions.
The original version of the driver, even with the Select button filtered, definitely had sporadic issues with input glitches. My updated version was nearly perfect after filtering the Select button. I'm pretty sure the Acknowledgement line implementation is what did it. I'm pretty confident in that one.
However, the Arduino reader is 100% perfect. So far I've needed no filtering, it all just works. I need to work on the CPU usage of the driver though, still, but for what it's worth, it should work on the Pi. Just plug the Arduino in with USB.