The $800 kit probably includes valves and lever linkage that's designed to fit on your tractor. For example the rear remote kit for my Branson has valves that bolt to the rear transmission housing where the hydraulic feed to the 3pt bolts on and a set of levers that mount to the floor of the operator station next to the seat. Between them there's a set of levers and pivots to make a linkage.
You can install your own valve on the fender or bolted to a bracket on the ROPS. The hoses are fairly simple once you understand the concepts and can map them to your tractors plumbing.
The other option, since your splitter has its own valve, would be to install a backhoe loop with quick connects. This lets you break the chain that goes from valve to valve and insert additional valves (a backhoe has a whole stack of valves). Normally it would go between the loader and the 3pt. That's a matter of figuring out which is the loader valve's power beyond port (it's usually connected to a hose that goes to the back of the transmission area), and adding quick connects to it (and probably some new hose as well). The splitter's valve is probably rater for more GPM than the tractor flows but you'd want to check to be sure.
With the loop you'd stop the tractor, disconnect the loop and plug the splitter into it. Then do the reverse when you take the splitter off. You have to keep the loop connected otherwise the pump deadheads and the 3pt won't work.