As already mentioned, the Burmester amps are typically designed with balanced-only inputs, have unusually low input impedance, and run at very high gain. This makes them difficult or impossible to run properly with many tube preamps. I am making a device called the Flex-Connect that overcomes these obstacles and allows any tube preamp to run these excellent amplifiers properly. Please see my website for more information.
Best regards,
Steve McCormack
SMc Audio