Digital volume attenuation is not the same as a preamp. Yes, it lowers the voltage, but it doesn't sound as well as good headphone amp pre-outs. However reviewers such as Sandu from soundnews noticed D70S works very well as a preamp with speakers.
I understand the benefit of distortion+volume attenuation of an analogue pre amp vs only volume attenuation of a digital preamp. Though those are probably fighting words that one sounds better. The distortion is already way below hearing so not an issue either way.
My concern is that my amp is a purifi eval1 I built and according to the review it goes to max volume with only 1.5 volts (I haven’t been able to test as waiting on passive speaker delivery). So with 5v at 0db, it will be running rather low for normal listening. I guess as the toppings have half steps all the way to -100db it should work fine.