Re amplifier - would it connect directly to the 3 OUT and 4 OUT of the op-amp or does it need to be after the capacitor like the stereo jack?
Re line out - wouldn't the existing stereo jack and circuit work for line out or would I need a different jack and circuit?
yeah, just use the lone out jacks... wasnt sure if you were keeping them.
Id connect the amp right at the jack, after the caps.