@GreenGL writes:
Can't say I'm aware of a national Volvo club? Did the wattage of the factory radio get upgraded in the rebuild too?
The quarterly magazine, "Rolling", is sent to members of all the official Volvo clubs in Australia. In fact, the multi-talented @carnut222 is the editor of this excellent publication.
Craig (from the SA Volvo club) does conversions of Volvo OE tape decks to MP3 / USB input for an extremely reasonable price. You can buy a unit for him and he also will modify your existing unit. He may be contacted at csrasmussen [at] bigpond.com with that and other questions about increasing the audio output power.
FWIW, I plan on replacing the OE tape deck in my 242GT with one of Craig's modified units.