You can install a windows AirPlay client on your htpc like shairportw and then use MC live loopback function to play the audio through MC and it's dsp.
I just tried it out, and it looks like
Shairport4w is probably a better option than Airfoil Speakers.
I did not realize that the Airfoil Speakers app on PC/Mac required an Airfoil license - I thought that was only for the transmitter, not the receiver. (the iOS receiver app is free)
It also seems like it may be more reliable - I've actually found Airfoil Speakers to be quite unstable, though Airfoil itself is fine.
Setting Shairport4w to use a 250 frame buffer seems to keep it in sync with all my other devices - though you can increase it to 500 frames if sync/latency is not a concern.
With MC20's WDM driver, you would be able to configure Shairport to play audio through Media Center.
P.S. I had to run the application as an administrator to configure it the first time.
Running it as a user and granting it elevated permissions just quit the app instead of opening the advanced settings.