Welcome to the PriusOnline forums. I hope you find a home here.
In answer to your question, many people have installed their own sound systems in their Prius. There are certain installations that would have more integration than others with the existing display systems. You will be able to find the answers to your questions with just a few simple searches in this forum. If you have some specific questions after reviewing these posts, go ahead & post them, and many folks here would be happy to provide help.
That sounds fantastic. I'm thinking if doing something similar (sub, ipod).
Did you do the work yourself, or go to a shop?
So, you're powering all the "regular" speakers in the car from the stereo, and the subs from the 200W? Are you able to get distortion-free loudness from the stock radio/speakers to match the level of the subs?
If you're in the bay area I'd love to get a listen.
Well, the bay area is over 1,500 miles away...hmmm...sure...road trip! Just kidding, but it wouldn't be out of the question...
Adding the subs has taken alot of "pressure" off the the stock speakers, since they really do poorly in reproducing decent bass.
I've turned down the bass level on the stock radio to one notch below half and the treble is maxed out.
As far as the subs go they are pretty well-matched to the stock speakers/radio output. Plus, I've installed a volume knob in the small blank knock-out panel to the right of the dimmer that controls the signal level going to the sub amp, thus with varying bass in all my songs, I can always turn up or down the bass level, matching any 'loudness' of the stock speakers.
Good luck on any projects you do. This car is as normal as anyone I've worked on, so be bold. I've done my own work on car systems for 15 years now. The Prius is great, but customizing it makes it greater.
Any other questions just ask. I love helping out in the Prius world.