The Audi S8's optional Bang & Olufsen sound system, a 14-speaker, 1,000-watt, twin-amplified mega-system that floods the cabin with crystalline sound and aural imaging that is a bit hallucinatory. Who knew you could get a whole chamber quartet in the back seat?

The B&O system is astonishing in many ways -- it is, for instance, astonishingly loud. And, as is traditional with B&O, there's a bit of theater involved. When you start the car, small cylinder-shaped tweeters rise out of the dashboard. These speakers use Acoustic Lens Technology -- I can't really explain it here, but I thought you might savor the name.

In another way, the B&O system is typical, as more luxury carmakers hook up with companies known for their audiophile home equipment.

Lexus, for example, has a co-branding arrangement with Mark Levinson (a division of Harman International). The Mark Levinson Reference Sound system in the LS460 is a sonic Howitzer: 450 watts, 19 speakers, 15 channels.

Likewise, Acura enlisted Grammy-winning producer-engineer Elliot Scheiner to develop sound systems for the RDX, MDX, TL and RL. These systems combine multi-channel playback with high-definition DVD-Audio.

But, as far as I can tell, the B&O system in the S8 has the most horsepower (wattage) of any factory-installed audio system.

The importance of wattage is hotly debated among audiophiles. It's generally understood that high-watt amplifiers have lower distortion at lower sound levels. It's also true that there is a disconnect between wattage (a linear scale) and sound pressure (logarithmic). A 1,000-watt sound system at max volume is not twice as loud as a 500-watt system, all other things being equal. It is, however, loud enough to make your brain exit your ears.

Here are two rules of thumb as you shop for high-end car audio. First, more speakers are better. The more speakers, the more uniform the sound field created in the cabin, the more optimized the signal to any individual speaker, the better the surround-sound spatial imaging and the finer the tuning of the signal to the cabin's acoustic properties. Second, by the time you reach that stage in life when you can afford a six-figure luxury sport sedan, your hearing is lousy, so don't fret about the first rule.

The trouble with high-end audio in automobiles, of course, is the source material.

FM radio, for example, has frequency response (the range of sounds able to be reproduced) between 50 hertz and 15,000 hertz, well short of the 20-hertz to 20,000-hertz range of conventional compact disc recordings.

Satellite and high-definition radio are better, but you have to pay monthly for the former and have limited station options with the latter. The high-density digital recording formats -- DVD-Audio and Super Audio CD -- are expensive and their music catalog limited.

In five years, the in-dash six-disc changers that are de rigueur now will be rendered obsolete by a variety of portable media, from iPods to USB flash memory. So, rip your Golden Earring CD while you can.

What won't change is that the quieter the car, the better the sound. The current generation of high-end audio systems spends much of its bandwidth competing with the ambient environment. Despite all the noise abatement built into the S8 -- the air suspension, acoustic glazing, girder-stiff aluminum chassis and 100 other details known only to Audi's oscilloscopes -- the cabin still has a minimum 60-decibel sound level. Quiet, yes, but not quiet enough.

The best sound systems on the road -- found in the Acura RL and TL -- use active noise cancellation, a technology that produces signals 180 degrees out of phase with the background noise, cutting down aural clutter. Bose, which pioneered the technology, is putting it into its own high-end OEM systems.

Hey, what do you know? I'm in Orange County already. Why did I come? I forget. I guess I'll have to turn around and drive home. It's half-past 10 and I'm shifting gear.