This style of abrasive would work when the machine was build to revers the spindles a very simple fuction when the spindles where run off an frequency inverter. Even older style Pro or machines like the CD2-300 moulding sander from QuickWood would be very easy to convert over to reversing of the spindles so the double side brush could be used with 2 different grit abrasives.
Now when you want to revers a spindle with out a frequency drive or a machine that uses a mecanical inverter for the changing of the speeds of the spindles, that would be the RO series from QuickWood the conversion would take place at the motor. We know that when two wires in a 3phase motor is changed the motor will run in revers. This will change the directions of the spindles and reversing can be used for Ro models also.
Call your local QuickWood representative and see if you machine can be made to use the double sided brush so you can use the two different grit abrasive.
When using two different grit abrasives on the machine a better pre sanding and sealer sanding can be done with the correct grit. No more changing abrasives for different sanding applications.