If you have 2 pumps each one delivering 200 Liters/minute at 3000 psi and put them on the same output line you will have 400 liters/minute at 3000 psi; basically you double the quantity but the pressure stays the same. In the particular case the precharge is the minimum you need to stop the plane.
If you have a chance, after checked chocks on, switch off the hydraulic pumps and start pumping the brakes, you will have around 8 to 10 available brakings with 3000 psi available, but once you reach 1000 psi on the gauge you won't have more than 2/3 left.