You got it right, the quaternion data is sent as OSC messages with the format:
/Chordata/(name_of_the_bone) <,ffff> [ quat.w, quat.x, quat.y, quat.z]
#the <,ffff> part is the OSC typetag, in most implementation you won't have to deal with it.
Unfortunately there's still no explicit documentation about this communication (it was suposed to be included in this document, but it was never finished)
We are currently working in a complete consolidation of all the docs to be published together with our upcoming official release. They will include detailed explanation on how this and others protocols used in the chordata system are structured.