Welcome to the forums! I'm curious what your overall goal is here? Do you NEED to rip out the PAMUX I/O? I ask because one of the great things about Opto 22 is how we support many of our legacy hardware brains, etc. so you can save the expense of replacing the I/O, wiring, etc. in many situations.
For example, we have PC boards and toolkits that support PAMUX on modern operating systems, like this PC-PAMUX-SDK.
Is EIP a requirement? Is speed of communication w/the I/O important? Tell us more! Usually there are many options and we've love to save you as much time/effort by giving you as many ideas and choices as possible.