2014 Pruis 3 package sound upgrade?

I plan on upgrading my stereo on the Priius. The three package has a descent stock Head/Nav unit (alpine?). So I am wanting to do a partial stereo upgrade for under $1000 parts and labor.

Has anyone dropped in a amplifier? i was thinking of a JBL MS-8 with a sound processor or recycling my 11 year old JL Audio amp but it is only 4 channels? He did mention putting in some dynamat behind the door for sound dampening.

Any suggestions on what to do for maximum sound quality on a budget from Prius owner?