Roon can’t control the preamp as it connected via an analogue (rca) connection via the naim. I presume you could enable digital volume control in roon of the naim.
Not sure how to set up the Roon extension, but that route seems most promising. It looks like it can run on a Raspberry Pi instead of my Roon server, which is not close enough to run a USB->RS232 connection to my preamp.
We have no mechanism within Roon’s functionality to provide control of arbitrary external devices. This would be possible using a Roon extension and as you’ve noted one has been developed which appears to solve this exact problem.
The extension developer should be providing all of the necessary documentation to get the extension setup and interfacing with your core. There’s also a fair amount of discussion of extension and Roon API topics over in the #tinkering:roonapi category.
Roon tested means the device is used via usb and using it’s own DAC. You have bypassed all of that and are using it as a purely analogue device, so bypassing all of the roon testing.
Reading @ged_hickman1’s comment above, just made me wonder…
If you’re thinking of using a RPi to solve this issue, why not just connect a RPi running Ropieee directly to your McIntosh via USB. That way Roon can both directly control it’s volume, while passing a digital PCM signal to your McIntosh for it’s DAC to decode.
You’ll might turn your nose up at this as it effectively eliminates your Naim and I expect you have a preference for using the analogue output of your Naim if you currently have it connected that way. But if it solves your volume control issue it may be worth trying (as I expect the lack of volume control is really annoying) and I can’t imagine the DAC in the McIntosh is too shabby, you may even prefer it to the Naim.