Using an ouboard DAC with SONY HAPZ1ES

I have a Sony HAPZ1ES, and want to try using an outboard DAC (using the USB).  I was thinking about the Ayre Codex because it can decode both PCM and DSD, which are the files stored on tbe Sony.  Anyone try this DAC with the Sony, or any other DACs?  I was also thinking about the Border Patrol (I’m more of an analog guy, although tbe BP wont be able to play my DSD files.  Not a huge deal.)
Any USB based dac will work.  Just make sure you have the latest firmware update on the Sony.
I’m trying to see if anyone with the Sony has seen improvement with an outboard DAC over the internal DAC.
The Sony sounds great, I’ve tried an outboard DAC.  Was a little diffferent but not better.

now, I would like to see Sony offer quboz support.  It is a high res player after all.  
I tried my HAPZ1ES with a Wyred4Sound Dac-2 DSD SE DAC and preferred the one in the Sony better.  Music seemed to flow better and with the Sony and there was more body to the music.  The Wyred dac seemed more in your face.
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There was a discussion earlier about using outbound DACs for DSD/SACD playback and my understanding was you need some specific connectivity arrangements to make it work. Don't remember all the details but should be easy to dig out. 
I've tried HAP-Z1ES USB into Oppo 205, Denafrips Terminator, & Marantz SA-10.  There were some problems with Terminator which uses Amanero USB interface, so it was returned.  I don't have any problems with both 205 and SA-10 which use XMOS USB interface. 

Eventually, I discovered the Z1ES limits the sound quality since I have 2 DACs which also have transport, so I can compare easily.  Not willing to spend too much money on player/renderer, I built my own using Intel NUC 7i5BNH with linear power supply and 2 internal SSDs, using Win 10 Pro with HYSOLID free player.  The sound from NUC into SA-10 DAC is much better compared to using Z1ES as player into SA-10, even after upgrading the Z1ES internal drive to SSD.
Interesting -thanks for the info.  I know that the Sony does some PCM to DSD conversion internally, and also will upsample lossy files (mp3, etc).  I think when used as a storage device only (external DAC) it outputs in native resolution.  That might account for some of the loss in body.
I have used tried an Auralic Vega DAC, Esoteric N-05 Streamer/DAC, a Bryston BDA-3 DAC, and am now using a Mytek Brooklyn DAC with the Sony HAP-Z1 in my home office.  I think all the DACs sounded better than the internal HAP-Z1 DAC.  Having said that, YMMV.