I want to use the unbalanced 2x4 box to take in a single LFE channel from a preamp and have the ability to set distances, gains, and EQ for up to four subwoofers on the outputs. Which plugin do I need to do this?

The best plug-in for this application is the miniDSP 2x4 combined with the 4way advanced. 

Here is a great application note to get started on this topic. https://www.minidsp.com/applications/home-theater-tuning/tuning-multiple-subs