You would want to max out your volume on your operating system, and control the volume from the amp directly if you can.
So with the k5 pro for example the switch on the left controls the input, so you would set it according to what input you would be using. The switch on the right control’s the amps gain, and you want to set that to adjust the volume levels of the amp. You choose a gain setting that allows you to have headroom to get a bit loud for quieter moments, but also make it so you have a decent amount of volume control. If you have the gain set too low, you will have to practically max out the volume control on the unit to get it loud. If you have the gain too high you will only have a little amount of volume control before it gets too loud. You want to choose the gain that gives you the best mix of volume and control
Personally I think it’s a good idea to set the bit dept at 24 bit and the sample rate at 96k