Though much of my current setup has been on a component-by-component upgrade, I recommend adding an aftermarket headunit (hu), an amp (or two), and speakers. But this depends on the available outputs on the stock hu. If it has pre-outs for an amplifier (s), and you like the hu, then you can simply add amps and speakers. If not, you will have to rewire and possibly purchase adapters to add an amplifier to your existing hu. If this is the case, then the sound quality, in most cases, lessens. Many aftermarket hu's have 4V pre-outs for the amplifiers, I'm not sure what rating Volvo has on their hu. There are a great number of quality car audio companies in addition to the mainstream brands. I suggest taking at look at www.elitecaraudio.com, www.sounddomain.com, and www.caraudioforum.com. You can post a question in the various forums, and many should happily reply. Also, you must take into account all associated costs for upgrading in addition to the components themselves, such as installation (if you don't do it on your own), RCA cables, power/gnd cable, speaker cable, and hu mounting hardware if you choose a half-din deck (what is found in your Volvo is a full-din unit). Good luck.

I read earlier on BB that the door speakers and the rear shelf speaker are run by the same wires. If that's true, then you got to pair of 8 ohm speakers in parallel, which makes the total equal to 4 ohms. It is just a theory, but maybe someone who knws the facts can elaborate. I have never seen an 8 ohm speaker in a (modern) car audio system.

The impedance of the speakers (4 ohm, 8 ohm, 16 ohm) must match the impedance of the output stage of the amplifier that is driving them to produce correct power transfer, and prevent output distortion. The amplifier in your car's stereo system obviously has an output transformer with an 8 ohm impedance, thus the 8 ohm speakers.....

Are you going to put in an aftermarket amp?

If all you want to do is change the speakers, then you basically have to go with an 8 ohm speaker back there unless you are willing to have someone play around with the wiring.

The first thing I did with my 855T is replace the head unit and put in a cd changer. I liked the stock look of the OE DIN, but I wanted true digital quality sound in the form of a fibre optic output from the cd changer in the glovebox to the aftermarket DIN.

I then put in an an 800W 5 channel amp to run the OE speakers and a 10" sub. However, with about 300W going to the 10" PPI, it obviously didn't last long.

I then put in Alpine DDDrive speakers throughout the car as well as upgrading to two 12" Pioneer Premier subs. I have also done quite a bit of sound insulation and wiring as well.

About the only thing I did wrong was get a too powerful amp before I got speakers to handle it. And then there's the shortened longevity of the alternator. Besides that, I couldn't be happier.

Pachabel's Canon never sound so hi fidelity. Trance never blew my mind like this before. Miles Davis never chilled me out so cool. Rock never hurt my ears like this before. And if you are the kind of person that has a problem with road rage, just put on some cool jazz or relaxing classical and you'll wonder how you ever drove without it.

About the only harm I have done to the car is a loosened tail gate panel which I have already permanently fixed. And because I got the box for the two 12" subs tuned for the car, I wasn't very much concerned with space. As a result, trunk space in my wagon is significantly lessened, but still easily large enough for two bags of lacrosse equipment, an emergency blanket, a first aid kit, extra strong snow brush, and other junk underneath the "security" cover I installed to keep the sound system out of view. It basically "fits." Rather humurous the way I become almost as efficient as many women are when it comes to packing when I have to.

As you can see, you start with ONE component upgrade, then another, then another . . .