I’m working on my own atm, it might be different from what you’ve found so far but kinda similar. (well, the user integration is missing but I think you can do without)
I’ve setup MyBB as forum software combined with MODx as CMS, the snippet I’m using for MODx is called MyBB Bolt-on and even though it’s 5 years old it still works (safe from 2 parts). For me the type of integration MuBB Bolt-on provides is perfect. I’ve posted about my findings earlier today, have a look
http://modxcms.com/forums/index.php/topic,10376.20.html (it also contains a link to my test setup). I’m currently just testing it a bit but so far I’m glad that just about everything is working
(hopefully I can get the events and userinfo to work as well)
But that will depend on the type of integration you want, for my site I’ll have the news and replies all via the forums + the snippet allows me to put the latest forum posts wherever I want them to be. So basically normal visitors will just need a forum account for replies / discussions and the actual site admins will have a MODx account.
So, if that’s what you’re able to work with then have a look but if you need account integration then SMF will be the better choice. Although I have no idea what other capabilities the SMF integration has, I prefer MyBB so I didn’t look much further then the MyBB bolt-on snippet
I guess that my opinion is kinda biased because of that lol
