Thanks to everyone for their input. I'm pleased to report progress...sort of.
Yesterday, I loaded one of the PT Sample files (F Blues) to test that the keyboard was receiving on multiple channels (which it is, as previously reported yesterday). Thinking about this overnight, it hit me that I was getting the specified instruments in the sample file (piano, bass etc.) Today, I loaded that same file and found that if I changed patches on one of the tracks, the change was recognized by the keyboard. So I deleted all the data from the sample file and saved the resulting empty file as the default template to be loaded when the program starts ($options.seq).
Now, when I start PT, it loads the $options file. I find I have to send one of the patches to the keyboard to get it to play in the associated voice, but once I've done that, other patches work fine; I can record, change instruments, edit etc. and so far, all has gone as expected.
There are some anomalies in other tracks that weren't part of the F Blues file, but I can work with what I've got for my modest needs (I think).
I'm not sure why this works, but I'm not going to argue with success:-)
Thanks again to everyone for their suggestions. You definitely helped me to get to know MIDI and my keyboard better...
Barry