You don't need anything extra. JRiver has its own parametric eq that is extremely flexible.
From the menu, click on Player > DSP Studio
and then, in the left menu, click on Parametric Equalizer. I am using it to smooth out some room effects in my desktop system, and it works great for me. Very transparent!
Hope that helps.
Mike
P.S. I agree, the lack of real documentation is an issue with JRiver Media Center. The Forum can be helpful. The Wiki can be helpful too, but much of the information is outdated.