Looking for quiet CPU coolers

You are somewhat limited by the type and size of case your media center uses, I'm guessing because you currently are running a Hyper 212+ this case is not tiny. If you are looking for a very quiet air cooler checkout the Noctua NH-D14 or NH-D15 (make sure your case can fit these as they are quite large (but very quiet).

Alternatively, you could investigate water cooling, as these are typically quiet as well, Corsair offers a nice arrangement of sizes depending on your cooling needs, although relatively quiet, they are not the most quiet closed loop water coolers due to the fans that come with them, which could be replaced with specialized high static pressure/silent fans of some type.

You may want to investigate the case ventilation as well, as this could drastically affect the performance of your Hyper 212+. If you don't exhaust enough heat from the case, the temperatures can build causing the Hyper 212+ to work harder(louder) attempting to displace that heat. This solution could be as easy as ordering some silent high air flow case fans and adding them to the case. At bare minimum you should be using at least a single exhaust fan near the top of your case. Adding a intake fan near the front of the case would increase cooling to this setup substantially creating a "wind tunnel". Also make sure that your case is not locked up in a tight space with no circulation, as this would also drastically effect cooling performance.

And lastly, for a super cheap solution, you could simply replace the noisy stock fan on the Hyper 212+ with a high flow silent fan of some type, just ensure the size matches what is on the Hyper 212+ and it is able to mount on it some way. There are many fan review sites that compare SPL (loudness) with performance (air flow) so you can find the best solution for your problem. And at most this would set you back $25. You could also add a second fan to the back of the Hyper 212+ to increase airflow and cooling as well (one fan pushes air into the cooler, while the fan on the opposite side pulls air out "push/pull"). If you choose this route, replace the noisy stock fan at least.

And lastly-er for the cheapest solution, you could check for dust buildup on the Hyper 212+ fan/heatsink and clean it out.
You could (depending on motherboard) adjust the fan speed or "target temperature" for your CPU within the BIOS as well.

Good luck!

The Phanteks TC-12DX is especially quiet in my experience if you set the PWM curve correctly.

Your case is a great one. I was simply making sure of it.

Are sure the noise you're hearing is the CPU fan? Not a wobbling HDD for example.
Did you monitor your temps? Are they fine? Maybe thermal is not very well applied anymore.