Hi all,
I've come to the conclusion that what I was looking for doesn't exist. In the hope of saving another neophyte a couple of hours of fruitless searching, here are my conclusions. Needless to say, if I'm wrong I'd be happy to be corrected!
1. There is no way to connect a SiriusXM tuner to a non-XM Honda OEM radio and maintain control over the channel selection from the OEM radio. You can attach a so-called dock & play Sirius or XM radio to the AUX input of the OEM radio, but this has the disadvantages that you have a fairly ugly radio attached to your dash or hanging from an air vent, you have visible wires dangling inside the cabin (i.e. power cord to lighter socket, audio wire to the back of the OEM radio, and antenna wire).
2. There are two options, (1) swap the non XM radio for a Honda OEM radio that is marked XM on the front (mine is not), or (2) swap the non-XM radio for an aftermarket radio that is XM ready, of which there are many choices.
3. The problem with (2) (2) is that you lose steering wheel control of audio and channels unless you buy an adapter, and you lose the existing subwoofer unless you add an amplifier. Considering this option, though, took me a couple of hours because if you think about replacing the OEM radio, you then need to decide whether you want a radio with Apple's CarPlay (Alpine or Pioneer), whether you want to install a rear camera given the possibility that a new head offers, and whether you wish to display Nav information on the screen of the new radio, v.s. looking at Nav information on your iPhone or iPad.
4. I've come to the conclusion that Sirius XM for me for my RL is not worth the hassle. What I've done instead is to buy a USA Spec BT45-HON3 adapter that will give me excellent handsfree telephone operation and music via my iPhone. I'm going to install an audible reverse alarm which I think is better for me than a rear camera. This way, I retain steering wheel control of the audio and radio, and retain the subwoofer, and there are no ugly wires in the cabin.
5. Your mileage may differ, but if I'm wrong about there not being an easy and relatively inexpensive fix to the problem please let me know!