Volvo's came equipped from the factory with Alpine CD players\remote changers that use the M-bus protocol. Any new Alpine remote changer with the CHM prefix will work e.g., CHM-S620. The problem with using an Alpine branded unit is that the Alpine connectors are different from the Volvo proprietary connectors found on your car. If you do use a branded Alpine unit you will need to purchase an adapter that will allow the Alpine cables to plug into the Volvo control unit. These adapters are available from a number of different companies. When the factory Volvo/Alpine remote changer in my Brick tanked this year I bought an Alpine M-bus protocol six-disc unit (CHM-S620) and a VOL-ALP adapter made by Peripheral Electronics (web site address: www.peripheral-aamp.com). This adapter allowed me to hook the unit up with ease. The adapter plugs into the back of the control unit in the dashboard and connects to the cable provided with the changer unit. I did have to run a new cable to the rear of the car, but this proved to be easier than I first anticipated.
Another option available to you is to buy a Volvo unit that is made by Alpine. If you do this it will plug into the existing harness without any modification. If you decide to go this route, your best, and cheapest, bet is to find one of these units on e-bay. From the dealer, they are about 700 bucks (ouch).

If your Volvo was not equiped with a cd player from the factory you will have to install a FM Modulator between the radio and the cd player. This will allow you to control the cd player using the existing fm radio. If you go this route, you can use any brand cdplayer you want so long it is compatible with the FM Modulator.

Hope this helps and good luck.