atma-sphere mp-1 and Colibri vdh cartridge

I am having problems with the output with the colibri. VDH said it may be incompatible with my preamp. I was hoping there was someone else that may have or tried this combo. and can shed some light on this. I have a very low output from the .85 mv XCP VDH. So low that I need to turn the volume up to unacceptable levels to use this cartridge. Since this cartridge has 4X the output of the existing cartridge I find this very strange. I presently have a .24 mv ZYX r1000 cartridge that works great (the zyx is a very nice cartridge, very underated by the audio community), there is a step up transformer in the preamp, installed by Ralph. After speaking with VDH on the phone he said first this step up transformer may not work with his cartridge, something about the loading impedance. Not being a electronic expert it was hard to follow his explanation. any help would be greatly appreciated.