I have a mag 256 with a couple of providers. I get stutter on some but not all of the HD channels on one of the providers. I gather mag boxes need continuous streams to work properly. Its a hard one to pinpoint but assuming all channels come from the same server you are connected to and only some of the HD channels stutter, I would say its the source thats the issue. If you have stuttering on all HD channels, it would point to your internet connection and/or proximity to the server. The easiest way to prove the latter is to try and connect using another means e.g. kodi or android app

It would help if the mag boxes had some sort of freeze detection software in which it is able to quickly recognize freezing and auto refresh the channel until it normalizes, this would only work if the whole process is smooth.

Have you played around with the pre buffering in settings, maybe set to 5ms to see if it helps.

I also have some stuttering with 3 of the providers I've tried also some are better than others and that is with 720p.

try to change your dns to google dns: 8.8.8.8. it usually helps.

I've manged to resolve 99% of the issue now looks like both the last providers were shit, 3rd one seems best :)

Try new update