Well, the Rosinni’s streaming board has a pretty powerful ARM Cortex A8 CPU which has plenty of computing headroom. Neither Roon/RAAT nor Mosaic/UPnP (or even FLAC decompression for that matter) is going to “stress” it at all 
In a proper setup, meaning if there’re no bottlenecks on your server platforms/networking, then objectively, streaming via Roon and Mosaic will sound identical.