Input Impedance for VTL MB 450 Signature

Hello. I have a pair of VTL MB 450 Signature monobloc amps with the Super Balanced Upgrade. These amps are not the new series II amps. I am using the VTL 7.5 preamp and have just purchased a pair of Vandersteen 5A speakers. I need to know the input impedance of the VTL amps (total input impedance - sum of positive and negative in a truly balanced amp) in order to set the external crossover for the Vandersteen 5A speaker. The other question that arises is if the VTL Super Balanced Upgrade is truly a balanced circuit. Thanks for your help.
Why not get in touch with Bea at VTL and ask her directly? Though always very busy, she is also very kind and helpful. Add the Serial Number of your amps, when mailing. You might have to wait for a few days for an answer.