I have the D1 and run the RCA outs to my Audioengine A2's. They are powered speakers so they have an amp built in to them. I have no problem with the two working together. The D1 has a headphone amp. It is my understanding that the RCA outs do not run through the amp, only the DAC.
I was pretty sure of this, but, not wanting to give bad advice, I just routed the D1's RCA cables to my Schiit Asgard and played a tune. It worked just fine (although, I have to say that the Bifrost was more impressive sounding than the D1's DAC).
Hope that helps.