Dev,

Maximum power transfer is relevant only where a load requires a lot of power (eg. Speakers). Using normal length line cables be it in studio or domestic use the terminating impedance on the receiving end is around 10K or higher and is meant to be a "bridging load", in other words a load that consumes virtually no power (referenced to a 600 Ohm "matched" load).

The 600 Ohm termination is needed if balanced lines are made several hundert yards to miles long. In this case we are dealing with a fully terminated transmission line where things are different.

If you raise the output impedance of your preamplifier above the neccesary minimum all you do is to lower the corner frequency of the lowpass formed by the preamplifiers output impedance and the cable capacitance (plus amplifier input capacitance which may be non-linear signal modulated) and you leave yourself open to problems from the high impedance interacting with grid-emission currents (or their transistor equivalents of base/gate current) and such currents are related to the signal in a strongly nonlinear fashion.

Hence all else being equal the lower the output impedance of a preamplifier the better.

Ciao T