Which volume control to use, DAC or amp?

What would the proper volume settings be for my system? I have a Xonar Essence DAC to a Yamaha integrated stereo amp. The amplifier volume knob is set to 11 'O clock and I adjust listening volume with the DAC only.

Can this be causing strain or be harmful for the amp to continually be at 11 'O clock?

Does the volume level setting of the DAC affect sound quality?

What would the ideal volume combination be, for the volume control on the DAC and then the amplifier? In other words, have the amp volume lower but the DAC higher, or the DAC volume lower and the amp volume higher?