Some more developments here in 286 land.
I decided to try harder to get an IDE --> CF doo-dad working as a slave drive, because there was no reason it shouldn't. Initially I thought that perhaps the 4GB CF I was using might be too big - although in theory I should just be able to use as much as the BIOS could handle - but I had no more luck with a 64MB card. Finally it occurred to me that the existing master drive, a Seagate ST351AX, might not be playing nice, and some googling confirmed that it has a relatively complicated jumper arrangement which required me to specify that a slave was present (see diagram below).
Once I'd set that the CF slave was detected and works as you'd expect. I love the CF-as-a-slave setup because it lets me move all of the interesting stuff off the 25 year old mechanical drive, and back it up easily to my main PC (and then the cloud). It also meant that I didn't need the Gotek floppy emulator anymore, and I could go back to enjoying the sights and sounds of a real 3.5" floppy drive.
I've also been messing around with slow-down utilities and not being 100% happy with the results. This machine has a turbo function which under-clocks the CPU to 8MHz, and that in theory is the right speed for California Games, Double Dragon, etc. But it was still noticeably too fast. The solution was to add a wait state via the BIOS; now with the turbo off, SI reports that I'm bang on the speed of an 8MHz machine (where previously I was 1.5 points higher), and the afore mentioned games play as expected.
And finally I added in a MusicQuest MQX-32m, so that I can drive my MT-32 when the time comes.
Some pics of my adventures:
Life? Don't talk to me about life.
