I also use an ES-9 with multiple sound modules in Windows. It’s a bit of a pain but there are ways around this limitation. Here are 3 options:
– Jack Audio. This is free but I was never able to figure out how to make it work.
– Voicemeeter. Also free & has a lot of features, but the routing is counterintuitive and sometimes stuff crashes.
– Dante Via: not free ($60) but it’s awesome and it works exactly how you’d want this kind of thing to work. It can see all of the programs accessing your audio as well as all of your drivers. You use Dante as your main audio driver in VCV & then just drag-and-drop connections in Dante between audio devices (including the ES-9) and programs (in particular, VCV). I use it all the time with VCV rack, Ableton, and my ES-9 with no issues. It’s great.
My suggestion is to try the various free options first. If they work for you, great! They did not work for me so I eventually bought Dante Via and I love it. Good luck!