You can look for a "10v reference". Those will output 10V, can be had reasonably inexpensively (either as boards or single parts, based on a 30-second eBay search), and should work so long as you're not drawing much current. That's what I was going to use to control my spindle until I decided that avoiding analog would be ideal (it's a servo, so quadrature input is what I ended up going with).
If a 12V supply will let you adjust it low enough (or a 9V supply high enough), that will also work, and you're not going to harm it at all by doing so unless the manufacturer did something really strange. That's probably the easiest approach.
Series diodes should also work as long as you don't have varying loads. Not a fan of that solution mostly because it's not "right".
If you're up for soldering, plenty of adjustable regulators out there- eg
www.digikey.com/en/products/detail/stmic...ronics/LM317T/591677
You can probably find breakout boards for something that will give you 10V by just changing a resistor.
All that said, I would leave it as-is if it's working- the fewer parts/wires/etc. the better IMO. It's your machine, though, so if you think 0-10V would be better or you'd have fun doing it or something, have at it.