I just lay a large pillow down and tip the box and sub onto it. You might have to find something to grab a hole in the sub to get it out. Depends if it sticks in there or not. I got some dental type picks that make so you can take them out easier if they are really stuck in there. Sometimes you can "tap" on the opposite end of the box when the sub is tipped to help loosen the driver too. The gasket tape from parts express can really "glue" them in though and that's when you will need a pick or something else to pry them loose.I’ll take them out.
How do others take out the driver? Just tip the box?
Like @BassThatHz mentioned I wouldn't expect a lot out of a single 12" with 375watts. I have a B&C 18 with 1000watts plus and it would take around 4 your 12" to equal that so I think you might be expecting too much from a single 12. You might have to bridge that amp and run that to both 12s once you get them finished if you still want more output. I am not familiar with your amp and what it actually puts out vs advertised power.