Ah...

My 1990 744T has the amp under the driver's kick plate. I had a single speaker woe and installed an EQ and consequently learned a bit about it.

If you have aftermarket speakers, don't even try the stock amp- sell it for 25-50$ on Ebay or something. New amps and speakers are strange, and I think Volvo used mostly analog with some transistor amps. They sound awesome on volvo speakrs, but I think would sound wimpy on these new high-demand speakers. Measuring the output wattage on the stock amp is not proper (and I haven't a way to do it), but the wattage would be somewhere around 25W/channel or 12.5 per speaker. yeah, wow, but new amps and speakers rate power differently.

The amp is connected to the back of the radio via a ROUND DIN shell connector. This is a connector with 9? pins surrounded by a metal shield. The EQ functions on a similar looking item, with a different number and arrangement of pins.

Either way, you are not going to want to or be able to connect your stereo to your amp without lots of splicing yourself. The DIN cable has all the wires (I think it is 8 for some reason) inside it. You would need to trace each pin, cut the head off, and splice the deck's pre-amp wiring to the chopped DIN cable. The original amp might be ideal if you're using volvo door-speakers, but a used radio might be better.

I have one with no tape function (I needed a tape component thx to my stupid friend) that I can test and sell you if you want. The tape player decoder cards have parts that process sound, even if the tape mechanics are useless. The type is TD6141 I believe. This indicates the 614 (radio type, probably meant for 4 speakers?) plus a 1 to indicate an onboard EQ (simple Bass/Treble and speaker front/rear on levers, with push-twist of the volume knob to adjust side-side balance).

I hope this helps.
-Will
1990 740T