The fact that you got no answer for over a month probably is your answer. Plex will "direct play" or transcode automatically. You have no control over that or most other aspects of your system audio. Plex is all about convenience. I run it so non-technical family members can access our music/video/photos server via a simple interface in their Mac browsers or our TiVo and Roku boxes. I use different server and player software for myself. Plex may be enough if you jack headphones directly into your Mac. But with most external DACs you'll hear a clear difference using players that cost money. Mentioned most often on computer audiophile websites are Audirvana+, HQPlayer, JRiver, and, yes, Roon. Also Amarra, but it is a work-in-progress.Try the trials.