I got an Amazon Fire TV a few weeks ago, and since it’s running a customized version of Android, it’s not too difficult to modify the system software to do exactly what you want.
I had a clear goal in mind: I wanted to be able to access recordings through my Plex server, watch live TV, and also access Netflix, Amazon Instant, YouTube, and HBO GO stuff from one box.
For Plex & TV, the clear answer was XBMC (soon to be known as Kodi). Thankfully, they have a fairly easy-to-follow installation guide for the Fire TV. The trickier part is setting up XBMC for live TV — that requires tuner hardware (I’m using a Ceton InfiniTV 4 so I can get cable channels) and a server to handle DVR and tuning duties (I’m using MythTV). Getting MythTV set up is its own huge blog post, so I’ll return to that sometime in the future.
The Fire TV doesn’t by default allow a different app to take over the “home” functionality, so I ended up following this thread over on XDA Developers (XDA is a great resource for tweaking Android) to work around that limitation.
The one major thing I learned is that the Fire TV, even though it includes hardware support for a variety of video formats, does not include support for the format used in broadcasting live TV, and changing channels was extremely unreliable. Following the steps in this post on the XBMC forums to turn off hardware acceleration for live TV only worked wonders.
To get Plex content, you can either use the official Plex app ($5 in the Amazon store) or the PleXBMC video add-on for XBMC (active support thread here). The Amber skin (available in the XBMC repository) boasts full Plex integration, so you can use the power of XBMC’s skinning & live TV support with your available-everywhere Plex library.
I’ll have some further follow-up (my experience getting MythTV running, other options for users, and how the box’s experience is going a few weeks in), and feel free to ask questions if you’re wondering about specifics.
My initial conclusion: the setup is a pain (especially MythTV), but it’s a far better experience than your cable box.