The T25, and my T233 and T293 have a factory kit to add one rear remote, (same kit may fit others in the same horsepower range). I'm looking at adding a second factory rear remote on the 293. Hydraulicly, it will stack on top of the one I have installed with just longer bolts. From a hydraulic standpoint you could stack them up as far as you want, by using threaded rods instead of bolts. But, I'm not sure there is room beneath the seat, without raising it, for more than one, and I'm not sure how to route the control handle, which on the one valve just stick out under the front of the seat.
The T233 is an open cab, and I'm considering adding a second loader valve in the hydraulic line from the stock loader valve to the rear remote valve, with the cable-controlled handle mounted in the right fender, to run a top and tilt setup. The two tractors have the same fenders, and the 233 has smaller rear tires, which leaves quite a bit of room under the fender for the valve, and hoses.
There was a guy on eBay who had bought the inventory of a closed TYM dealer, and had the factory NIMCO loader valves, for $175, NOS in the box. So, I bought the two he had. He also had a rear remote valve for $150 so I bought it thinking I can stack it on the rear remote valve in the T293, to run top and tilt on it.