Hmmm, here's what I'd look at:
"Second attempt = Setting up only Faderport under Setup/Peripherals/MIDI Controllers page. Faderport is #1 - Type set to HUI, Recv/Send set to PreSnsFP2.....Play/Stop buttons work on the Faderport. And its Prev/Next buttons could only change between my Click track and channel 2 on the mixer - weird"
This should be correct, but you left out the 3rd item after the send and rcv ports. That box should be set to 8(thinking maybe you have it set for 2)
"Radium 49 is now set up under Setup/MIDI/MIDI Studio Setup. Manufacturer set to Generic MIDI. Model set to Generic MIDI. In/Out ports set to LegacyKbrd. Send/Recv channels set to ch16 (Radium 49 set to ch16 as well)."
This is the correct place for proper setup, but I'm not sure you have the correct settings. In and Out ports(assuming the Radium is connected via USB) should probably look something like "Radium 49 USB[Emulated]". Send/Recv channels should be all ON(all channels in blue) for send. Recv probably doesn't matter as you won't be sending midi data back to the Radium. Lastly, I would set the Radium to OMNI or ALL midi channels if you can. If you can't, then I would set to use midi channel 1.
Last thing to check: Under the VIEW menu, hit MIX windows shows>Instrument(so Instrument has a check mark). This will add a row across the top of the MIX window showing you(on Instrument tracks) what source Pro Tools is looking at for midi data(signal from the Radium), as well as what VI plugin it should be feeding(for a new Instrument track with a freshly-added plugin, it will usually make the proper connection by default. But if you maybe changed your mind and deleted 1 plugin and then added a new one, the assignment may need to be manually set). Also, put the Instrument track into Record-ready or it may not make any sound when playing the keyboard