I bought a nice, used, carbon frame bike from an esteemed member of the Tarheel TrailBlazers community.  I've come to realize that the wheels are standard Deore XT equipment.  

There are no markings on the rims, only the hubs.  The front hub is HB-M756 and the rear is FH-M756A.  The only info for rim size is the tires; Maxxis Ardent EXO 27.5 X 2.40 on the front and 27.5 X 2.25 on the rear.  The power train is 1 X 11 with a Shimano cassette.

I would really appreciate recommendations for wheel upgrades.  I see that there are MANY new and used wheel sets on PinkBike.  I'm thinking of budgeting around $400.  

Thanks for any advice that you can provide.

how much do you weigh? what type of riding do you do? 

Most everyone can benefit from some decently wide rims (internal width) which gives more tire volume allowing you to run lower pressures for better traction and plushness while still maintaining decent sidewall support. Ideal rim width will depend on the tire width you plan to run, but anywhere from 25 to 30mm internal would be good for the tires you are currently running.

Most everyone can also benefit from some quality hubs with sealed cartridge bearings and a good freehub with a high number of POE (points of engagement). Some people swear by Shimano's cup/cone style bearings, and while there is a valid engineering point to be made about being able to fit in larger ball bearings to improve durability. I personally feel like that benefit is outweighed by the added difficulty of fiddling with loose steel BBs (dropping on the floor and disappearing forever) and properly setting the bearing preload when servicing. Plus if the cup race gets damaged the hub is basically scrap. Cartridge bearings can be cleaned out and re-greased if they are not badly worn, but it is also pretty easy (and cheap) to just replace them outright.

Actual rim strength and spoke count/lacing pattern will depend mostly on rider weight and intended use. 

For your budget, I would recommend looking into a set of Stan's wheels. Arch of Flow rims depending on your requirements. I have no experience with their new Neo hubs, but their old 3.30s were decent. Many people also swear by Hope Pro hubs as well for that price range, but again I have no direct experience with them.

Flows would be a good choice for you, they are a little heavy but should easily be able to stand up to the abuse.

If you can swing it, there are some really good deals right now on Industry Nine Trail 245 wheels. They are on closeout because the 24.5mm internal width rim is being discontinued and replaced with a 27.0 mm IW rim. I9s are legit. They are hand made here in NC, with big fat aluminum spokes (extra stiff), and some of the best hubs in the industry.

Or you can go custom and lace up some Stan's flow rims to the hubs of your choosing. I hear there are a few guys on this forum that are highly respected wheel builders that might be willing to take on your business. 

Wheels are one of the best and most noticeable upgrades you can make to a mountain bike, right up there with suspension. It is the kind of upgrade that is worth spending as much as your budget will allow. The performance payoff is worth it.  

Whatever you go with you're going to want a 32 spoke wheel for strength. 

Other considerations, what is your axle setup? I assume it is not boost? so 100mm wide in front? Is it thru axle or quick release? 

215lbs here, too, and I'm not easy on wheels. Currently running a set of Spank Oozy 345's with Hope Pro4 hubs, 32 spoke, built by Mark at The Cycle Path. He built up virtually the same combo for my old bike, too. I liked them so much, I had a new set for my new bike before it even left the shop. They perform flawlessly, take the abuse I dish out, and I never worry about if my wheelset will hold up when I'm out on the trail.