MAC based prioritization

Hi

Looking for some advice on configuring MAC based prioritization for my home network.
Either give my Roku boxes (running streaming Netflix, Amazon, Hulu) priority over rest of traffic, or give the one machine running sabnzbd (download from newsgoups) lowest priority.

When downloading and watching Netflix, Netflix sometimes rebuffers, and sometimes switches to lower quality.
If I pause the sabnzbd download, no issues.

I have seen references to L7 scripts for prioritizing Netflix, but I also run other streaming services on the Rokus, so I figured it is much easier to prioritize all traffic to/from the Roku’s by MAC address.

Any examples or pointer please?

P.