If you want to use a FLIRC-remote with Lumin (or any other device/zone), you could do this with a RaspberryPi running Roopieee and a FLIRC-receiver. Setup is really easy and it works quite well. If you want to proceed in this way I could give you the details of how to get it to work, since I had this setup for quite a while.
IMO the better solution for controlling Roon is this:
I have used this as soon as it was available and couldn’t be happier.