setup as requested:
Roon Bridge: MacBook Air (latest Sierra OS 10.12.3), Audiolab MDAC plus (latest firmware 0.020) connected via USB to roon bridge.
Roon Core: iMac (latest Sierra OS 10.12.3), DSD music stored (mixture of ISO & DSF files format) via USB connected to roon core, other PCM titles stored on Synology NAS.
Wireless Network connects roon core/bridge.
Audirvana installed on Macbook Air has no problems with DSD playback…
I see there is a user with the same DAC and posted a request for him to share his settings…though i am not sure whether the mdac+ is connected via roon bridge or core. I tried emulating his settings to no avail too.