The original focusmax used MaximDL. I remember this from years ago. It does not run "standalone" because it would then need its own camera control software. Download a version and try it, if you can get it to run at all.
The issue of getting really good single star focus seems to be at the heart of your ask. I think that what may not be obvious is that you will have to make a full switch over to something else like the SKYX to make FMAX 4 a good choice. Otherwise you will need to be shutting down SGP whenever you want to focus your telescope. You will then need to start up the SKYX or MaximDL, connect to all of your devices all over again and then run FMAX. Maybe you are OK with this but it's not a trivial changeover.
I would recommend the SKYX rather than Maxim DL because if you buy Professional you get the use of Image Link and the SKYX own one star focusing routine - @focus2. With MDL you also have to buy Pinpoint to be able to plate solve. Plate solving is really useful with FMAX. That's because doing single star focusing requires finding a suitable star. FMAX4 has the "Acquire Star" routine where it runs a query to find appropriate (magnitude) stars, slews to them, focuses, and slews back to your target all automatically.
I run CCDAP on top of either MDL or SKYX so that I can focus periodically, when the temperature changes, or when I change filters. You can't really do that without some additional automation program.