There’s a thread here that discussed the setup that I used. You need to dl the minimserver app to your QNAP. Install minimwatch on your computer ( for me it’s a mac) and set the stream transcode configuration to “flac:L16”. There might be some other details. I’m heading in to the office and will try to find it later.
Edit- this is the thread I think. It’s kinda disjointed but should get you there.