Impedance mismatch?

What potential problems, if any, could exist with a tube pre (output imp: 600 ohms Balanced) and a "Class-T" amp (input imp: 300K ohms Balanced)? TIA.
none - that is a huge difference.
Hasse, the higher the load's input impedance, the easier it is for the source to drive. One looks for a minimum 1:10 ratio of driving-to-driven impedances, and higher (= 1:20, for instance) is better.