Ok, that's what I thought. My situation is the same, disc version and installer won't run.
There are many old installers that just won't run on Win 10. It's nothing to do with the installers being 32bit, they are compatible and run on any other 64bit system perfectly but not on Win 10.
The problem is tracking down what stops them functioning under Win 10 as any fix can vary installer to installer, PC to PC. Some installers there simply is no solution to get them working.
Win 10 is terrible for running old software. I've spent a bunch of time getting certain games running under Win 10. I may try to find a solution for the DC9 installer at some point. I'm debating running FS9 on a Win 7 machine and ditching Win 10 for FS9. I'll see how many things don't run well and decide from there. As soon as I read your post I immediately tried my DC9 as I had not attempted to install it yet under Win 10. I can now add it to the Win 10 problem list.
If I come up with a solution for it under Win 10 I'll let you know. Even if I do, no guarantee what worked for me will work for you on your system.
Then once it's installed, who knows, having it work properly and the gauges working properly under Win 10 might be another matter altogether. It never ends with Win 10! haha
Best fix option, get a Win 7 PC for FS9!