Also, can anybody tell me anything about impedance matching between pre- and power amps?
In general you want the input impedance of the amp to be 10x the output impedance of the pre. BUT, the impedance varies by frequency and may go higher or lower than the stated number, so to be safe I’d look for the input impedance on the amp to be at least 20x the preamps’s output impedance if possible. In general I think this is more likely to be an issue with tubes than solid state. Hope this helps.