This answer will be pretty lengthy, but I also have a new 2520 on order and it took a while for me to understand the various ways you can set up your tractor.
The tractor comes with a bank of 4 remote hydraulic couplers just under the right hand floorboard. These are used to connect the 4 lines from the loader, which then allows control of the loader through the Joystick.
Independent Lift, is a separate cylinder, which must be installed on the tractor, that will allow you to raise and lower the deck, independently from the 3PTH. In order to operate this "Independent Lift" cylinder, you must connect the 2 hydraulic lines to two of the ports of the remotes. If you do this, the deck will be raised and lowered also by the joystick control. This means you must disconnect 2 of the lines that would normally come from the loader, since the loader uses all 4 ports to operate all the functions.
JD sells a kit which is another set of couplers, that mount alongside the existing 4 ports, (Which then gives you 6 couplers) which will allow you to keep both the Independent Lift (for the mower deck) and the 4 lines for the loader connected at all times. In order to divert the hydraulic fluid to each implement, a "Diverter Valve" is used, which is part of the kit, and as I understand it, has a push/pull controller, which is mounted on the inside lower fender, where the operator can just pull or push it to divert the hydraulic fluid to the implement he wants to control.
Without a "Diverter Valve" kit, if you are using your mower, you would have to get off the tractor, and switch out the 2 lines controlling the deck to those that control the loader when you want to use it, because you will only have 4 remote connectors.
I opted to use the mechanical lift (3 PTH) to lift my deck, instead of the "Independent Lift" so I won't need this diverter valve. This means that I will raise and lower my deck with the rock shaft (3 PTH lever). I also opted for the "Deck Lockup Kit", which will allow me to lock the deck in the up position, which will thereby free the 3PTH to operate normally, with the deck locked up.
I also wanted to use my loader, and deck at the same time. To do this, it is much more economical to use the regular mechanical lift for the deck, otherwise you will need to buy not only the "Independent Mower Lift" kit, and if you want to keep all hoses connected at all times, you must also but the "Diverter Valve" kit, unless you want to switch hoses around every time you want to switch from mowing to loading.
In my case, by the time I bought both kits and had them installed, it was going to add $1200 - $1500 to the cost. I know this sounds expensive, but us Canadians always get hosed on the accessories.
I hope this helps explain things. I know I had a hard time understanding it, especially when most dealers immediately wanted to sell me the Independent Lift kit right from the get go.
REV
REV