Pros: Small speakers, big sound. Great clarity. Loud. Simple connectivity. Convincing Virual 5.1!
Cons: Expensive, very expensive... _ few niggles.
The bottom line: Excellent speakers for the customer who needs a set of 2.1 speakers that will look good, and have minimal footprint but offer a close to 5.1 sound.
Background
I bought and still own the Bose Companion 3 system. I really liked the Companion 3 system for computer speakers. Infact a HiFi buff heard them, skeptically, and he was impressed.

I needed a system that will offer good sound in a small amount of space. The companion 3's delivered.

However I was looking for a new computer not that long ago, when the Bose companion 5's arrived. I was interested to hear what they had to offer.

I was able to get a fairly good price on them so went ahead.

Features

TrueSpace signal processing offers a close to 5.1 sound from 2 speakers and the bass module

Pod control offers easy connectivity and control of system volume.

Acoustimass delivers bass that offers a powerful, rich musical experience and a vibrant movie sound with powerful explosions.

Active System Protection protects the system at high volume.

Pre-installed speaker stands that offer optimum positioning.

USB connectivity for the best sound quality and 5.1 processing.

Sound

Well what can I say?

Over the Companion 3 they have so much more clairity. The instruments are more defined and natural. However I also know the Companion 3 Series II offers this improvement.

The spaciousness and stereo sound from the Companion 5s is also better.

The sound is slightly more tinny on the Companion 5. I feel because of the port change in the Companion 3 > 5 it has affected the bass response for music. Movies however do have enough bass to feel more like a cinema.

The Acoustimass can be weak at times but you can change the Acoustimass volume on the back of the unit. The bass is tuneful and quite rich.

The sound is very good for the size and I feel the system is more about quality than blasing the walls with bass.

The USB offers the Companion 5 the best possible sound from your computer and I have found it to offer better sound than a CD source using the line in on the POD.

They sound especially good for movies and jazz/classical.

The 5.1 virtual sound

It's lifelike thats for sure. It's never going to match a real 5.1 system but using the Windows Vista speaker tester you can actually hear the sound move around you. It's weird.

Listening to movies is especially real on this system - I would say it's as close as any system could ever get to producing the sound of a 5.1 system.

My thoughts and opinions

The system is easy to use but I did find a few twiggles.

The volume on the computer is default on installation of the Bose audio (in Vista anyway) quite low and required to be turned up to get the full sound. If this is a Vista only issue I'm not sure.

The USB can limit the length the acoustimass module is from the PC.

The connectivity of a non-PC device to the C5 was through the Control pod, I didnt like this for a permanant installation, I wish Bose would have put another AUX/line in

The speaker can get tinny at very very high volume. I wish Bose would solve this, the old Companions were the same, but I guess it's such a loud volume anyway!

The USB connection will only work on a main port that is USB2 enabled. Most new computers are.

Other than this I found them excellent speakers. If you just need stereo the new Companion 3s a fine.

Technical

The technical details of the Bose are not shown anywhere on the website.

However upon inspection it appears to use a similar driver to the Companion 3 which is a 60watt DVC. I would guess it is redesigned slightly due to the new re-tuning on the port. It's a dual voice coil loudspeaker by the looks of it and looks pretty high excursion.

Port noise is about the same as the Companion 3s at very, very low feq. which is acceptable as it cannot be heard at all with music, it becomes evident with 20-35Hz tests.

The twiddlers in the arrays, are around 12watts x2 offering 24watts total output per speaker.

I cant comment on the C5 as I have not tested it's full freq. response, but the Companion 3s had around a 40Hz - 15Khz.

I expect it to be quite impressivly increased with the Companion 5, more so on the treble.

I think thats about it....

My overall opinion is try them if you want a speaker system that will give you a near 5.1 experience without wires and speakers everywhere.