Roon sounds like it would be great for you - but you'll have to spend some time and money on setting it up. I have all my music in lossless FLAC on a Synology N

Roon sounds like it would be great for you - but you'll have to spend some time and money on setting it up. I have all my music in lossless FLAC on a Synology NAS and run the Roon server on there. The Roon client should work on your phone and connect to your RME ADI-2 DAC as well (great DAC btw, I'd really like one myself). It handles lossless streaming, and ensuring the digital chain is optimized for quality all the way to your DAC. It can also apply arbitrary parametric EQ on the server side, in case you want to use some EQ profiles for your HD800s if you don't have the RME handy.