Can't figure out how to get 5.1 out

is Link group still working?

Link Groups are functional on my systems.

when I go to the Link Group page, its all grey out and I can't group anything

If the Audio Track Format is anything but Mono, the source Audio Tracks will be greyed out in the Link Group window.

Confirm that your source Audio Tracks are in the correct format via the Track Index
(listed as 1.0 in the Format column for Mono).

Including a system spec (preferably in your signature), with Operating System and Resolve version may assist: viewtopic.php?f=21&t=90190#24

I confirm that everything works fine, even under Windows 10