On page 8 (3rd pic down) it shows the see-through diagram of the fender and hoses. Hose "D" runs from the top of the transmission which is I'm almost certain is the relief valve assembly for the main pump from what i'm accustomed to seeing, makes sense being on top of the transmission case too. The line "D" runs from that up and around to the right hand side of the remote valve. The return line off that remote valve curls down and is plumbed into the loader valve and that port is marked "P" on the loader valve for the pump or pressure, whichever it means.
Page 7 (first photo) the elbow 12 and connector 15 are normally connected with a high pressure steel line and was remove to mount the valve. 12 is again, from the relief valve bank, and 15 right into the loader valve.
They are pretty generic on what all these connections are for but looking at the tractor and the instructions its coming pretty clear.
I bought the valve with a relief that was set at 2000psi, and thats in the range my tractor reliefs are set too. I guess i'll run it and see if the valve suffers any issues. Its funny the factory way isnt quite the "right" way to do it. There is a "tank" line right below the pressure port on the loader valve so routing a PB valve woulnt be that much more work.
As for using the 3pt while using this valve. Im not sure what you mean, im sure the 3pt would work, but the remote vavle would likely take priorty over all the others as its first in line. Its even before the loader valve. Its the first valve in line to receive pump pressure.