JBL system w/out NAV doesn't sound as good as JBL w/ Nav system

[Oops -- I meant for the header to say "...doesn't sound as good as JBL system WITH nav"]

[Yes, I've done a search in the forum -- haven't found what I was looking for...]

Just got out of my 2010 Prius IV with Nav into a 2011 Prius IV without Nav. Both had JBL audio systems, but the system that was paired with the nav system was much better. (My error -- thought since there were both JBL that the audio portion was the same.)

At any rate, I only seem to find threads on upgrading the non-JBL systems.

So -- is it worth it to do some simple upgrades? I am pretty limited on budget, so I was wondering if changing out the door speakers (only) would be worth the trouble/$'s.

I also have an 8" sub (already in enclosure) and amp from a previous car, so that would certainly make an impact, but at the moment I'm more concerned about the sound quality up front. It's just not as clear/strong sounding as the old system.

Anyone have a good suggestion?

Thanks.