But if you're feeling technical and comfortable in your ability to fix your steam link should something mess up then you can flash the 337 and 341 builds manually with a USB drive, see the S01config script in /etc/init.d/startup in there you can see how to change your update branch to dev and flash the dev images. Once again I'm being ambiguous just to avoid hand-holding anyone into messing something up. All in all though the two dev builds don't hold anything useful to the public, the 341 is fairly interesting with its error message though.
Also 04_2015 is a valid hardware branch, but I doubt any of those SystemUpdate images will cooperate on our public 06_2015 hardware. Tinker carefully my friends.