thanks for the warm welcome and the replies!
So, it looks like I got this working.
First, I followed a few dead ends:
- I got both the windows configurator and the parallax windows tools to load under WINE for Linux. However, I couldn't get past the need for USB drivers, so those apps couldn't connect
- I had a good look at the source code for the propellent program. However, it's written in Pascal, and would probably take too much effort to make independent of windows.
- Next I tried a number of serial terminals to verify the connection and the communications with the mount, but there were no clear ways to upload
What I did next was to start looking more generally at options for the firmware for the processor itself. On the parallax site, I came across an old tool called 'BST', and a command line loader called 'BSTL'. There are windows, Mac and Linux versions. The apps are old, i386 builds, but I got them working in Ubuntu. The link from the old website supporting them is out of date, but hunting around the website you can find a link to an updated build.
BSTL has done the trick, I think. I've uploaded the latest firmware and it's reporting that updated firmware over the serial link. KStars is connecting via INDI. I looks like clear skies tonight, so hopefully I'll get to give the mount it's first try-out tonight!
Another route I didn't investigate that also showed some promise is a C++ Library called PropellerManager. That looks like it could be easily integrated with some cross-platform apps as a general communication tool. It also looks like Parallax have a wifi updater as well.
If it's useful, I'll do a summary of the steps I've taken to get the mount up and running under linux. It's not actually that hard when you know what to do, it's just finding the right combination of software and configurations that takes some research.
Bresser 130/650 Newtonian Reflector
QHY 5II-C CCD
Controlled via Ubuntu 18.04 running on an old MacBook Pro