Prius is Toyota, Honda is either an Insight or Civic Hybrid. I own a 2004 Prius with premium sound system so I can tell you some on what I researched.
First here are the specs.
Base Head Unit Specifications
• AM/FM Tuner
• CD Player
• DSP (never made it)
• Amplifier Power: 40 W × 4-Ch.
• 6-speaker System
• RDS function
• Manufacturer: Panasonic
Premium Head Unit Specs
• AM/FM Tuner
• Cassette Player
• In-dash- 6-CD Changer
• ASL (never made it :-/)
• RDS function
• Amplifier Power: 45 W × 4-Ch.
• 9-speaker System
• Manufacturer:
JBL (Amplifier, Speaker)
Panasonic (Head Unit)
Speaker Specifications (base - 6 speakers total):
Front Door
Tweeter: 3.8 cm (1.5 in.) 4ohm
Full Range: 16 cm (6.3 in.) 4ohm
Rear Door
Full Range: 16 cm (6.3 in.) 4ohm
Speaker Specs (JBL premium - 9 speakers total):
Instrument Panel Center Speaker: 6.5 cm (2.6 in.) 2ohm
Front Door:
Tweeter 2.0 cm (0.8 in.) 6ohm
Full Range 16 cm (6.3 in.) 2ohm
Rear Door
Tweeter: 2.0 cm (0.8 in.) 6ohm
Full Range: 16 cm (6.3 in.) 3ohm
From what others have said, the premium systems is fine, just need to add a woofer. However the only way to add a woofer to it is to get a line level converter, connected it either to the rear door or center speaker wire after the amp. The front speakers have seperate lines for the speakers, one for the tweeters and one for the door speaker. The rear speakers have a passive crossover in the door somewhere, so the rear speakers and center speaker wires are the only full range speaker wires. The reason the line level converter need to be added after the amp is Im pretty sure that the amp handels the fade/balance/eq.
The prius puts out 14.1 volts always as long as the car is ready to drive, doesnt matter if you are idle, driving, gas engine on or off. This is regulated by the car itself, hence the "block" attached to the positive terminal of the battery. From what others have said, but I have never confirmed with toyota, is that the DC/DC converter (201v->12v) is rated at 100 amps. If you start to exceed this, the car will shut down unnecessary things like the PTC heaters (the heaters that warm the cabin before the engine warms up).
So in short, keep the H/U, speakers, and add a woofer. Also check out
http://www.priuschat.com
I havent done anything to my car yet, got a Memphis 16-MC1000D amp, still deciding on the woofer. If you have any more questions about the Prius, feel free to PM me and I will try to answer them.