Master in SDJ should be at 12 oclock. Then adjust each individual track volume(in SDJ) till into the yellow on software meters.....keep away from red ;). You only have to do this once per track as SDJ will save the level withing the mp3 tag. Also setting autogain on within the software will get you close so only minimal tweaking will be needed ;)

Then do the same on your mixer/pioneer DDJ SR.

Trim individual input "Trims" till input is correct level. Once this is set turn your master level so it matches the same level have set coming in via trims. Now keep your master knob at this position.

This will ensure that whatever level you have coming in to mixer will be what goes out to speakers(unity gain).

And if you kept it all correct at all stages you will have headroom so wont clips and distort signal.