No it does not have a headphone jack. Yes, it does have built in amplification.
It has 5.1 channel input ( yun ba ang tamang term dun sa may LF,RF, C, LS, RS inputs?). Anyway from what I understand and if i'm not wrong, the decoding is done by the dvds internal decoder and the promac just amplifies it. ( So di mo na kailangan ng seperate na amp)
I hope this answers all your question guys.