Hello,
I hope it won't be too late for you... I will have the same problem... I plan to upgrade my old Mac Pro 5.1 to Monterey with the Open Legacy Patcher within the next month..
Double tricky... ;-)
I'm just as crazy as you and love my old Digi 003
Weeks ago I found this driver helper for Digi 002/003, compatible with Big Sur and Monterey
https://neyrinck.com/downloads/digihelper/
Don't know yet if it will work...
if anyone out there has had experience with it please let me/ us know...
Best,
Helen