JL xd 600/6 is your best bet.
you want to drive those under seat's direct to the amp.
so yes, to answer your question bridge with 6.
however im sure there any other configurations, but this is the most popular.
also the xd600/6 is just literally perfect with our 6 speaker setup
also you will have to have the HU recoded to HIFI mode or buy a DSP to clean out the shite over eq'd signal.
there is a lot of DIY step by step on the AUDIO table of contents. Amazing resource.