At this time, we do not support casting Slingbox from a computer to a Chromecast (well, we support the idea, but our technology does not support it at this time). So, while you would most likely see the Chromecast icon on the Chrome browser, the Slingplayer extension (Slingplayer for Chrome) does not pop up with that icon.
Here is an article on the currently supported methods of watching Slingbox on a TV:
Now, that's not to say that all other methods of viewing on a TV WILL not work, but we cannot guarantee that it will work either.
Hope this helps.
Thanks Evan. I notice it works when using the slingplayer on my Android samsung note 4 but I would like to cast if from my computer because with the beta version of chromecast, it will cast in 1080P rather than 720P. I sure encourage you guys to try to allow it to work with chromecast when the slingplayer extension pops up. I don't have apple TV but I'll look into it as well as other devices like fireTV. Please let me know if you find a 3rd party windows based software that allows the slingplayer popup window to cast to chromecast. Thks very much.