80Gig MKV movie file. What's a newb gotta do?

You should read up here:
http://www.avsforum.com/f/39/networking-media-servers-amp-content-streamers

Get a Dune, Popcorn Hour, WD TV or any other standalone player. IMO better than relying on a BD player for MKV playback.

80gb movie? Where in the world would you get a movie file so big. Blu rays max out at 50gb, and even then the movies themselves rarely get much over 30gb (after subtracting the space for extras and such). I am actually pretty surprised the mac won't do 1080p, but the suggestions above are some good ideas. I would not bother trying to make a bd player work w/your files as I have heard most players either do not support it, or they have a hard time with consistant playback.

The Samsung we have does a good job playing just about anything I've thrown at it. If you truly have an 80gb MKV, I'm guessing it's super high bitrate, uncompressed DTS, basically as good as it gets. So, right off the bat, if you really care about keeping it at that quality (and I'm sure you'd like to), that leaves out almost anything generally seen as a "media player" or a "set-top-box" that most people would use. Xbox (as I learned the hard way) won't even let you play a video file over 4gb, and has horrendous bitrate caps on all video it plays, so that's out. Apple TV is better, but nowhere near your 80gb file. Nothing else in that category that I know of is, either. Not sure about PS3. Logic is telling me it has the power to easily handle it, whether or not Sony decided to arbitrarily put a file size/bitrate cap on what it plays is another matter. You could try buying a Blu-Ray player and seeing if it will handle it. Even the old Sammy I have will upconvert properly horrible files to 1080p/24, and make them look half way decent. I had some trash 480i files that it played flawlessly, without skipping a beat. All Samsung players support MKVs, not sure if there's a bitrate or filesize restriction but I doubt it. They'll also play nice with uncompressed audio. So try anything from them. Dirt cheap, plus you then have a nice machine just in case you actually pick up a disc or two, which is nice. Failing that, Sony just dropped a sub-$250 4k (!) Blu-Ray player, a quick google search shows it for much less than that on some sites. It will convert something all the way from 480 to 4k, and if it does half as good a job as the 1000ES (which apparently does an amazing job) then it can probably handle your 80 gb MKV. Hell, a 4k movie, even at the bitrates that we will see on consumer media is going to probably be at least that size if not bigger. So I would guess that the Sony could handle it. And you're certainly future-proofed for a while then too.