Control of the arms should not be an issue if the 4 screws are properly adjusted for your end use. Generally if one adds a pump, they add a reservoir as well to make a separate system. Integral oil supply volume is relatively small but is enough for the rams and a high pressure remote. Add-ons are typically low pressure, high volume multiple cyl.
A low pressure pump could draw from the tractor reservoir, go through your new valve, and connect directly to your lift rams, but the low pressure would drastically reduce your lift capacity.