I did a project controlling 72 servos on an arduino mega.
We used pololu servo controllers. They exist in different sizes, this one could do the job: https://www.pololu.com/product/1354. We also tried some cheap chinese controllers, I think they were called usb usc32, but they didn't work well.
You could use https://github.com/thomasgeissl/ardPololuServoController on the arduino side. I will probably update it to support the other protocol and other features.
We did the communication using OSC messages, https://github.com/CNMAT/OSC. Which was fine in our case.
Let me know if I can help you somehow.
Edit: https://vimeo.com/135904342 in case you're interested in the installation