also ends with "60" so I think it is the same series as yours. It probably shares the same Preamp circuit op amps.
"Yamaha RX-A860 Preamplifier Measurements
In the past some Yamaha AV receivers had weak output drivers in their preamp outputs where they didn't supply enough voltage to hit the magic 2Vrms, which is what most power amplifiers need to achieve full rated power. Sadly, it looks like Yamaha has taken a step backwards with the RX-A860. At 1.9Vrms output, the receiver shut down. When I checked at a slightly lower output (1.6Vrms), I noticed a pretty nasty FFT distortion profile. There simply is NO excuse for this in a day and age when opamps are cheap and supply voltage is plentiful.
Yamaha RX-A860 FFT @ 1.6Vrms.jpg
Yamaha RX-A860 Preamp Out FFT Distortion Analysis @ 1.6Vrms
Yamaha RX-A860 FFT @ 1Vrms.jpg
Yamaha RX-A860 Preamp Out FFT Distortion Analysis @ 1Vrms
At 1Vrms, the output looks much cleaner. If you're planning on using external amplification with the RX-A860, look for a power amplifier with a relatively high voltage gain (29dB or greater) so that it can achieve full rated power below where the preamp outputs of the RX-A860 starts clipping. For example, a 200-watt amplifier with a voltage gain of 29dB will reach its rated power at around 1.4Vrms."
Later, right before the conclusion:
"the preamp out section of this receiver is a bit weak, making it critical to match with a high gain amplifier to ensure the preamp itself doesn't clip while driving external amplification. "
Another possible work around would be to jack up the preamp level out puts with a device called a "line amp". It is sort of a "preamp post amp". AudioControl make nice ones I believe but by the time you get all your channels covered it may end up being better to just get a new, fundamentally beefier preout AVR or a prepro instead.