too high of an output resistance coupled with too high of an input resistance means not enough signal gets through?
No, the main problem is that neither impedance, especially the preamp output impedance, is likely to be perfectly constant with frequency. The amount of signal that is seen by the power amp input is dependent on the ratio of power amp input impedance to the total of the two impedances. Therefore if the two impedances do not vary with frequency in an identical manner, the overall frequency response will become non-flat.
Higher power amp input impedance and/or lower preamp output impedance will reduce the significance of whatever variations may be present in the impedance vs. frequency characteristics.
Tube preamps usually have an output impedance that rises considerably at deep bass frequencies (approaching 20Hz), due to the coupling capacitor at their output. That will result in reduced deep bass response if the power amp input impedance is not high enough. I see, however, that the PR-T1 is transformer coupled, apparently with no capacitors in the signal path at all, so that should not be a concern in this case.
Another effect that can occur, although it is usually much less of a concern, is that if the output impedance of the preamp is high at HIGH frequencies, and the capacitance of the interconnect cable is high (due to the cable being very long and/or having high capacitance per unit length), the preamp's output impedance and the cable capacitance will act together as a low pass filter, producing a slight dulling of the upper treble, and also resulting in transient response that may be perceived as sluggish.
Regards,
-- Al
