Good to hear the PLM is working. I would not invest more in a PLC. The PLC does not support Extended commands which have been in use for a few years now. There is no indication the PLC will ever be updated to support the latest functions/features that require Extended commands.
I have an EZX10RF at v1C. The internal PLM would be at a later level if you requested the product update service.
I know of no way to use the X10 Bright/Dim buttons as far as converting them to Insteon commands through the EZX10RF device.
There are no plans to update the SHN Utility to run natively on the Mac.