Mike I have been there, done that, and bought the T-shirt. Most valves can have a power beyond sleeve installed in the outlet of the valve body. May have to contact a hydraulic shop or GOOGLE for the answer.
Tying a remote back to power an auxillary valve is not the best way. It cause unneseccary wear to the valve, created heat, and limits your flow DRASTICALY! Even using the OEM remotes on a loader are SLOW, hence why I went through the expense and time to do it right. Not to mention the OEM relief if not worn is 1500-1600 PSI. I have my auxillary valve set to 2000 PSI, which gets oil first. Then the steering, then the remotes, which still have the OEM relief PSI. There is a higher PSI relief that you can install good for 2050 PSI and 2500 PSI, your choice for $260 at CNH. The same price as a new 3 spool Prince vavle
Myself I found a Prince 3 spool with adjustable relief on EBAY for about $240. Bought the power beyond sleeve elseshere for about $20. To keep from cutting into the OEM hydraulics, I shunted between the pump and flow divider. The only drawback is if you are cycling a spool on the loader the steering is hard. I ran the return to the IPTO fill plug (1 1/4" ORB threads).
Here are some pics of how I plumbed my system. I also upgraded the worn 12 GPM with a fresh 17 GPM. I also used 3/4" hose on the IN, OUT, and RETURN. I used 1/2" hose on the work ports. The spool valve is rated 25 GPM. My loader is faster than most new tractors. The loader is a Koyker 220, bought new.
Lower line is from pump to IN on valve. Upper is from the POWER BEYOND OUT on the valve.
Return line from auxillary valve bank, 1 1/4" ORB 90 to 3/4" MJIC.
Valve bank from the operators station.
View of valve bracket, work hose routing, and supply lines. Used 3/4" Parker quick connects without poppet checks (free flow). Used opposing male and female. Can connect the two lines into each other if for some reason I have to remove the valve tower. The loader work ports have their own 1/2" pioneer quick connects with poppets.
Tractor and loader in action!
Good luck! If you have any other 504 questions, contact me through the forum or email. I have learned ALOT about this little tractor and would be glad to share.
Charles