Halo CEA Maps?

You can play the MM off the disc without the code for Reach. It has it's own little Reach module in there, with just the CEA maps. You can forge and use the theater and play firefight. You don't need Reach at all to get the full experience. The only reason to buy a new copy with a code would be if you really wanted to see a CEA map in Reach MM once every like 50 games or so.

I highly recommend grabbing a cheap disc and playing it all - campaign, MM, FF - all superior to the rest of Reach's offering IMO. If it wasn't for the abysmal population and the limited playlist selection, I wouldn't have bothered with my Reach disc after CEA launched. As it was it was about 50/50.

Oh, and I think there are weapons you only have access to if you're forging from the CEA disc. So there's that.

 

I've built an Infection map on Ridgeline called "Favela Run" last Summer. I've tested it about 50 times (not even kidding!) with a core of players from my friends list who also had the Anniversary maps. It was really hard to find random players from Xbox Live that a) had the maps too, and b) actually accepted my invite. The reason why I was able to test it and play it this many times was due to lack and to the fact that my friends invited some of their friends too. However, everyone who played on the map had a blast and was really glad to see something else than Forgeworld all the time.

What I'm trying to say is that if you're willing to put a lot of work into getting people to play with you and have a lot of patience like I did, it will pay off in the end and therefore you can do fine playing it on the CEA disc instead of the Reach one. Even though the map was officially released only one week before Halo 4 came out, there was still interest for it: my friends liked it a lot, the map took 3rd place in the Hub of the Dead III contest on ForgeHub, and The Halo Forge Epidemic was going to feature it - if only Halo 4 didn't come out that soon already.
Even though I did play the map from my Reach disc, this didn't make a difference for who showed up: only my friends with the map pack could play it anyway and I invited the random players from the Anniversary playlists in Matchmaking.

Now that the fileshare systems are still down, I'm thinking about hosting BIOC lobbies in Halo Reach and Halo 3 every once in a while, so you can always ask me when I'm planning on hosting one of those so you might be able to join. I will also play maps from the map packs, especially Anniversary, such as my previously mentioned map as well as other maps that were made by guys like ZipZapZop and Cassel on the Headlong remake (Breakneck), so for instance I could play those first so you can start playing on your CEA copy and at some point quickly plug in your Reach disc once we're done with the Anniversary maps if you would like to keep on playing.
This is only useful information if you're an Infection enthusiast though, because otherwise it's pointless joining since I will only be playing Infection maps. But if you are, this could help you finding people to play the Anniversary maps with you.

So yeah, it depends on if you're patient and resolute to find players on the new maps only whether or not you should buy the used disc or just a new one so you can also play in Reach. But you can always join these BIOC lobbies if you can't find people on your own.

 

Headlong and Ridgeline aren't even in MM anymore, they cut it down to only one 4v4 playlist for Anni. If you play MM off the CEA disc, you'll be really limited. Shame... those were brilliant maps.

 

No I don't think you can. You can play the CEA maps on the Reach disc if you have the code, but you can't play the Reach maps on the CEA disc.