1:This is why thoughtful/concerned source manufacturers like Wadia, Mark Levinson, Bricasti and a few others have "gain settings links" on some of their upper end models in the analogue output stage, to limit the maximum gain. So then the digital volume control upstream can be used at 70% or higher, for any system.
2:If you don't have these analogue gain settings, the next best is to use a passive volume control after the source, and set the volume on the passive so the digital volume on the source can be used above 70% this way you can still use the source remote volume control between 70 and 100%
Cheers George