Devialet - direct NAS connection

[MIKE]

Here's another possibility - the user Audio Station is running under may not have sufficient permissions to access the audio device driver.
https://forum.synology.com/enu/viewtopic.php?t=91151

oooo shuuut!!

Yes - It could be the solution. I have not seen that option before (the column of "Renderer USB/DLNA" in user settings was to narrow and of course not activated). I will check it in couple minutes. 

Thanks, Mike

Rufus, You are the man!
it was not as easy as ABC but not a rocket science too  - here is the instruction manual for other users (Polish to English translation):

1. Synology / Audio Station / Top Menu / User rights - "Renderer USB/DLAN" (ON)
2. Synology / Audio Station / Top Menu / Advanced settings - "Turn on the high quality output for USB speakers" (ON)
3. Synology / Audio Station / Top Menu / "My computer" replace by "USB speakres" 
4. iPhone / DS Audio app / "choose the player" settings - USB Speaker

Works!! Perfectly!

Thanks a lot!

Reg, Mike