When you go through the head unit's audio options, do you have a DSP setting? Assuming it has the stock Alpine head unit it should have shipped with.
Failing that, behind the trim in the load space on the left side, if you have DSP, there will be a single large amplifier. If no amplifier, it either has door amps, or is driving the speakers directly from the head unit - which was only really found on more basic models (including the Bordeaux weirdly).
Southampton with a Nanocom for Thor/GEMS P38s
1996 4.6 HSE, then became a 4.0, now cubed.
1997-8 4.6 HSE Motronic/Wabco prototype vehicle. Now M57 powered. Still auto.