I want to install two of the boss low profile subs, one under each front seat, but what kind of splitter or adapter would I need to run two of them instead of just one.

Im kinda noob at audio stuff

 

Run two sets of wires where its necessary like the rca's and grounds but split the power and the remote turn on lead. If your deck doesnt have enough preamp outputs then buy the correct 1 male to 2 female connector.