WRECKA,
There are a few HU that have higher than 4v. Sony's new high end xplod HUs even have 5.5. Someone has a 6v if I remember correctly.
Sounds like you have a pretty good system to start with.
As for improvement. Everything you have is very good equipment and changing it will probably have neglible results in SQ. Even so, I would probably replace the SoloBarics with Lambda Premium Line Subs if you are looking for SQ. If you are going for SPL/SQ then look at Eclipse Titaniums or Lambda TD series (pre-orders are being taken at 249.00 ea.) If you are going strictly SPL, maybe consider DD, Kove, Eclipse Ti, etc.
If you want to get the same quality sub if not a little better, check out the Shiva at
www.adireaudio.com. You'll be able to sell the solobarics buy 2 Shivas and pocket 200.00 or so to put towards new door and rear speakers. As for the rear. Take the components out of the rear door and replace the CV in the rear deck with a pair of Jordan JX62s running a freq range of 300-4000 hz.
For the front speakers, consider making a set of components with a custom crossover or if you would like to purchase a complete system, check out the MB Quart Q series components, Diamond Hex, Focal Utopia, or Morel (best tweeters IMO) components, or Dynaudio.
