If you want to add additional spools and work ports you have only one "correct" option. That is to purchase a 1, 2 or 3 spool valve with power beyond capability and a relief valve. The
B7500 probably has a flow rate of just under 5 gpm for the implement circuit so that will determine your valve size.
You then plumb as follows:
1. disconnect the power beyond connection from the loaders hydraulic outlet block. Connect this hose to the input port of your new valve. Joining this hose with another to make the correct length is ok but you cannot tee into the power beyond.
2. connect the power beyond port of your new valve to the loaders hydraulic output block (where the loader pb hose went).
3. connect the output port of your new valve to the same place that the loader valve's "tank" port goes. This connection can be tee'd with the loader's tank port hose. The connection is usually found under the seat and goes into the transmission reservoir.
4. connect the work ports of your new valve to whatever (tnt, blade, etc) you want.
This effectively connects your new valve in series with the hydraulic circuit which is the principle behind power beyond.
Note that some of what you want to do can be accomplished using your loader valve directly by simply connection its cylinder hoses to something else.