How to best connect sub on $250 total stereo system?

Hey some units had been being built around my GF daughter:

Aiwa AV-D57 mainly for 2ch -- no preamp or processor audio output signal. Tried composite AV output L/R to L/R input of the sub described down below and realized they are just cover disconnected jacks. There's dedicated single sub output from the Aiwa. Does that mean that I can connect it to just one terminal or I have to use at least Y-connector? I can also use speaker terminals on sub, but hate fudging around those screw-on binding posts! What would be more beneficial after all using line-sub out or speaker terminals?

The rest of system:

B&W C201 speakers really need sub since they can struggle to work full range 

Infinity MSW1 subwoofer

Modest Technics SLD3 all stock turntable with Ortofon 2m Red.

Computer Audio with Mac Book pro 2013 and Fiios DAC 

Sony Mega 300 disk player

Wires and interconnects mostly car audio brands especially if it needs to be exposed for cool looks  :)