It is not a problem if the system does not hum in normal operation. Since you would never operate the system with just the amp on and not the preamp the question is moot. Most amps will hum loudly if you pull the IC out of the preamp and touch the signal pin with your finger. Is this a problem? NO, because this is not how the system is normally operated.
Follow Joe Abram's advice and you will never have any hum so you will never have a problem. Sit back and relax, enjoy your hum free system :>)
Follow Joe Abram's advice and you will never have any hum so you will never have a problem. Sit back and relax, enjoy your hum free system :>)