What is the minimum power requirement; is it 60W or 80W?
Over on Electronics Lab you said 60W.
This will be intended for car audio, so I need it to be moderately efficient, and I want it to be able to do between 60W and 125W RMS @ 2-4Ω.
Is that per channel or for all the channels combined?
If it's 60W per channel then you can't do it straight from 12V, you need a boost converter.
It isn't possible to put 60W RMS into even a 2Ω load, let alone a 4Ω load.
The peak power can be calculated using Ohm's law.
P = V²/R = 12²/2 = 144/2 = 72W.
The RMS power is half the peak power so 72W peak becomes just 31W.
This is at clipping, assuming negligible loss in the driver transistors, with it sounding terrible.
The only way you can put more than 31W RMS into a 2Ω load is to use a boost converter to increase the supply voltage. To put 60W RMS into a 2Ω load, the peak voltage must be 15.5V. There's always a few Volts loss in the driver transistors so the power supply voltage needs to be higher than the peak output voltage. For a 60W amplifier, you'll need an 18V supply.
I advise scaling it down to 12W RMS per channel into 4Ω and it'll need to be bridged otherwise you can knock that down to just 3W.
Many car amplifier companies lie about the power output of their equipment. They might specify it at clipping with a supply voltage of 15V and give the peak power for all channels added together, rather than the RMS power per channel with a supply voltage of 12V. Quite often they don't tell you this, they might just say "power output 100W" which is really meaningless.