As a bit of an audiophile, I guarantee you will not be happy with the sound quality using the built in 25 watt per channel amplifier, so if you care about how it sounds, be prepared to use an external amplifier.

About a year ago, I put together and installed a 4 speaker with subwoofer system in a 1800E. I used an inexpensive 4 x 200 watt amplifier that also had a 400 watt output for a subwoofer and it really sounded good.

The owner already had installed a Retrosound head unit and some crappy front and rear speakers, but a decent subwoofer. The amplifier didn't have enough power and the wiring was poor quality and too small.

2 areas NOT to cheap out on are the speakers and ALL of the wiring. For example, I used an expensive low level 4 channel RCA cable to connect the head unit to the amplifier in the trunk. That cable is made of wires which are done in twisted pairs like internet cable which increases signal strength and reduces noise over long distances. This cable also included the trigger wire to turn on the amplifier when the head unit is turned on.

IIRC, the cost of all of the wiring was more than the cost of the amplifier which was the cheapest component. Even the total cost of the speaker boxes was more than the amp.

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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com