JBL 9 Speaker System sounds muddy...

It's not so much that the Center Speaker is poo, but rather that it totally dilutes the spacial reality (stereo effect). It might not be so bad if the level was a LOT lower, but unplugging it totally is easy to do, and is a quick fix.

Another major problem, is that the "JBL sound" has always had "tizzy" highs (great for brass, not so much for strings). It is worse on the Prius than other Toyota vehicles.

Bottom line: the VERY FIRST improvement is disconnecting the damn center speaker! (As the OP found out).

 

Wow! I feel the JBL "premium" system is decent for a stock stereo and one of the better stock stereos in a luxury car, but it's definitely not "premium".

If you want to hear bad, try listening to the stock (non-Bose) stereo on my 350Z on the highway or my former 91 Camry V6.

I still haven't tried taking the plunge of unplugging the center. As for getting a sub, is it because you wanted more bass (I don't think it needs it) or non-muddy bass?

BTW, I'm no fan of Blose myself.