I think the RMHV is essentially the same as the DDCSV, and I don't think there is an option to use step/dir for spindle control. And I don't think the 0-10V is isolated. The only way you could get it to work with a non-isolated drive would be with a 0-10V to 0-10V isolator
Not sure what you mean here, would you mind elaborating please.. I used the pwm signal from my bob and the https://www.ebay.co.uk/itm/111654184682 to convert it to 0-10V isolated for the spindle driver board.