Gents, the Marantz SR 8015 is an 11 channel unit.
If you set it up for only 5 channels of amplification, and the remaining channels not connected, there is virtually no heating from those amplifiers. The power supply transformer will also run cooler as it will pull less than 50%. Excessive Heat does cause premature aging in electronic components, but the rule of thumb is running them cooler will also extend their lifespan. While I'm a Fan of external Fans (and have 2 on one of my Denons that I tend to drive hard once in a while),
@natra84 may not need them if he doesn't push those 5 channels very hard.
Just my 2 bits.