I believe the guideline is that the impedance of the amp should be at least 10X the pre, so at 45k its on the borderline.... I believe that my Bedini amp is about 45K Ohms, and it does work with my Aurieges but YMMV. Maybe one of the experts can chime in....
However, if you match with a tube amp, like what Jonathan said impedance matching is less of a concern.