Stock head unit 3from a personal point of view id change only the head unit for now as the marginal improvement over swapping the stock speakers with some custom ones is nothing compared to vast difference that swapping the head unit will make.
Hi bud,I disagree with the above (my opinion of course). The HU change was a 500% improvement, the speaker change and sound deadening were small, subtle changes. If you like your neighbours to know your coming home 5 minutes before you arrive, then go for an additional amplifier. The output from my Pioneer is much louder than stock and far more than my poor ears can cope with.
Subwoofer(s) are very worthwhile after a HU change, my Porsche has subs in the doors as standard and even though it has the same Pioneer HU as the Civic, I do prefer the sound in the Porsche.