You can play native dsd (dsf files) directly, I.e with phones connected directly to the dx-80. The issue is when you try to connect to an eternal amp or dac, as the coax out doesn't allow dsf file's to be played /transferred and the usb connection doesn't work as a usb out. The dx-90 did a conversion to from dsf to pcm, but the dx-80 doesn't yet. Maybe a later firmware update?
Quite frustrating! You would have thought a $360 music player billed as dsd ready would have been able to do these things....as I said in an earlier post, there is a gap in the market here for a reasonably priced player that covers all the bases. I still find it frustrating that you seem to need a phd in audio electronics to figure everything out....and a thousand cables and adapters to make things work as they should!
I have a few daps, including the dx-90, dx-80 and Cayin N6....I use each for different purposes, sometimes as portable rigs on the road, and sometimes connected to my home rigs, (speaker based and headphone based). I still spend a lot of time frigging things to get them to work correctly! Maybe I should start a cable business!