The best solution may be taking to the dealer and they can test what your machine is putting out in GPM and PSI. If you put a mulcher on it that info is important in setting up the mulcher for your machine.
One thing about putting 3/4 couplers on your Deere, you will need adaptors to attach anything that is half inch. I had those made up for my DL550, unless you change all your attachments over to 3/4. Its kind of a pain. Thats why having half and 5/8 is really nice. High flow coupler when you need it, but you still have half inch for everything else.
This is my personal thoughts, if your serious about high flow production, you really have the wrong machine. I would make do with whatever flow your machine makes. I would have it tested so that you know what those numbers are, but unless they are really anemic, I would deal with it. When you trade or sell that machine, I would choose different for more high flow performance.