What all does the hydraulic system need to power other than the drive motors for the saw and some cylinders?
I'm curious being that to make a single pump run multiple motors at the same speed plus supply auxiliary flow to a valve spools is not all that complicated nor should be expensive and I can't see where a hydraulic system that runs at 2000+ PSI would need much protection from outside water pressures of a few hundred PSI.
If it was me I would be designing the whole hydraulic system and its electrical components to sit inside it's own hydraulic reservoir tank and have that pressure balanced with the outside. All the electrical solenoids are oil insulated and the whole system is pressure balance with the outside making it possible for the tank to be light and cheap to make.
To bad you're half way across the continent away. I would love to do some hands on work and testing with this sort of system design.