Line Out RCA jack to?...............

I have an audio head unit I am wiring to an equalizer/booster. The wiring diagram indicates left and right outputs (+/-) stereo to the EQ/booster inputs (+/-). My question is, do i connect the audio outputs (R/L) to the EQ/booster or do I use the Line outputs to the EQ/Booster?

Depends entirely what it designed to use - but usually you would expect to use line outputs.

The audio outputs usually have a volume control. The line outputs are fixed level. So how you connect depends upon where you want to control the volume.