The setting on the preamp was less than 0 db, maybe -4db maybe less.
The Yamaha has a 6 ohm setting (which manufacturer states is also suitable for 4 ohms for the front speakers), I have been advised before here on the forum to stick with the 8 ohm setting; however, I have switched to the 6 ohm setting for the moment and it seems to be working better, still can't really tell until I have a free moment without the fam around to experiment a bit.
Before when I had the XPA 2, running the 663 at the 6 ohm setting did not trigger the infamous protect circuit on the XPA 2, but it wasn't loud enough for those moments when you want to crank up the sound a bit. Now with the A1400-2 the system seems to have plenty of head room on the 6 ohm setting, and the overall experience seems more smooth, e.g., as if the volume control increments on the preamp are smaller, making the "volume dial" more spread out, so to speak.
I admit that I did not think that the pre out section of the 663 would overdrive the inputs of a power amp even on the 8 ohm setting with volume output of 0 db or less (and it seems it would be immaterial to the preamp what ohm speakers are downstream from the power amp), so I am a bit mystified, however I lack time and inclination to do a lot of troubleshooting that might damage the speakers.
In addition the kicker for me was when the 663 shut down spontaneously, that just shouldn't happen under normal circumstances when reproducing material at 0 db or less, and suggests there may have been an overload within the preamp itself before possibly overdriving the power amp input(s).
