I just tried out the
Dirac Live Room Correction Suite software on my MacBook and I'm very impressed. I think this is something everyone should try out because it will help make sure your setup is performing at its best.
Using a microphone the software takes measurements and then lets you create audio filters to adjust the frequency response and impulse response. I used a Behringer ECM8000 microphone with calibration file and tried things out with both
Airfoil and a USB -> S/PDIF converter to bypass the MacBook's sound card and feed directly into my Neko Audio D100 Mk2 DAC.
I am running this in my 2-channel setup at home, but it also supports surround sound and larger venues like an auditorium. The audio filter adds a noticeable delay to the sound, so if you use a HTPC you will need to delay your video to match. The software has a simple on/off switch that makes it easy to evaluate the audio filter's effect.
With Dirac Live engaged, the music was more centered and the sound stage moved closer so its distance equaled my speaker distance. The frequency response was more balanced and there was less distortion. I'm so pleased with the result I intend to continue using this in my setup: MacBook (w/Dirac Live) -> Airfoil -> DAC.
I've attached my measurements and the predicted post-filter results for the left channel.

The original frequency response measurements for the nine measured positions.

The post-filter predicted frequency responses at the nine measurement positions.

The original measured average and predicted average frequency response.

The original impulse response measurements for the nine measured positions.

The post-filter predicted impulse responses at the nine measurement positions.

The original measured average and predicted average impulse response.