Hello. I am a Veteran Embedded systems designer with over 9 years in the industry for developing solutions for Industrial Automation, Machine control and Data Acquisition. I develop PLC & SCADA systems as well as custom embedded systems. Some of the projects i have done on freelancer and you can see in my profile.
I have not used Opto22's systems much, but i had the opportunity to troubleshoot a plant system that was based on Opto22's PACs some years back.
Since what you require is basically support for communication of the module(s) on ModBus, maybe i can help.
It will be best if we can probably hold an online discussion (preferably voice via skype) to discuss your requirements in detail so i may then come-up with the best possible solution for your needs. If you want, you may add me on skype where my id is the same as my freelancer profile name (TopGunPk).
Look forward to hearing from you soon.
Warm regards
Zeeshan A. Noorwala
Automation Engineering Solutions