I stumbled across this ocean energy conversion system.
It is designed to sit on top of a floating wave energy device but to me it should be able to be housed within a buoy.
The multi tethered Ceto 6 looks to me to be a suitable platform for these devices (or something similar).
The latest images of Ceto 6 do not show an external pump, so I assume the power take off system they go with will be quite different to what has been used in earlier models.