Cable "burn in"

You are right Jackcob....get burning. "Breaking in" a cable has everything to do with the insulation - not the wire itself. The insulation or dielectric will absorb energy from the conductor when a current is flowing (music). This energy absorption causes the dielectric's molecules to re-arrange themselves from random to uniform order. When re-arranged the dielectric will absorb less energy and consequently cause less distortion. The cable is now broken-in and sound improves. To ensure the cable stays broken-in it must remain connected and the components left on. If no signal is present in the cable the molecules will re-arrange into a random state and break-in will have to be repeated. Length of break-in varies from 100-500 hours.

the preamp doesn't usually have to be energized, but the input that you have those "cooking" cables connected to needs to be selected in order for signal current to be traveling through the cables of interest. If there's no load termination at the end of those cables, then no signal current flows & hence no breakin is occuring.
Most (rotary switch selector design) preamps terminate whatever input is selected, whether the pre is on or not. However if it's a relay-driven logic toplolgy, then power must be turned on to energize that input selector relay.
If in any doubt then checking the load termination with an ohmmeter will verify.

Yep, hooking a cable up to a tuner is about the cheapest way to burn it in.

KF