Ken,
Do you need the VDM module to control the Tunze's. I am considering adding a couple 6205's or 6305's to my system and am on the fence as to whether to control them via my Apex or just use the Tunze controller. What else is needed beside the Tunze adapter cables to control them via the Apex? Also, from my reading the Tunze's run at up to 18V for full power. Does the Apex variable speed control allow the Tunze's to go to full power?