I have the A90 with both VE-JV1 and VE-RD1.
The time to boot is very short (about 10 sec).
You have to consider the time to change boards. Open the door with screw driver, change the board and close the door again. This will take a time that makes impossible to be donne in stage from one music to the other. I'm trying to parallel these cards by a flat cable, with a switch to save time.