Well, the RF module has only been tested with Dakota Alert products. As far as Voice Alert – it may work, we don’t know (untested). If you do try it, we would love to know the results.
You cannot “tune” the frequency on the RF module for your Optex devices.
For your current Optex devices though, clearly the ideal is to use what is working for you. What receiver are you using? Depending on the receiver, I can think of two options:
1) If the receiver is triggering X10 events, you can look at using the EZBridge to have those X10 events control Insteon devices (using macros) – this may be a cheaper option for you than replacing all of your sensors.
2) If you are using something like an Optex 1000 receiver, you could use an EZIO module to catch the switch on the 1000 and send an Insteon command from action – again, a cheaper option than replacing all of your sensors.