Those all look like viable options. I have been looking at a power beyond loop or pinning open that valve. My only hard spot with either is the flow rate from the tractor's hydraulic pump. Kubota lists the L3400 as having 7 gpm for the flow, which I wouldn't think to be enough for a 20T logsplitter. I have been entertaining the thought of a PTO hydraulic pump, but that seems pretty cost prohibitive when compared to the cost of a free standing gas unit.....
I checked out those dual directional splitters, they look pretty cool. Do you get the same amount of splitting force in both directions, I guess it should be equal. I think that running QC's to the splitter off the pinned open existing valve is a good way to go. Separately, how difficult and/or expensive is it to install a power beyond loop? What other implements would require PB?