FEW people recommend 10 gauge wire from the panel. Depends on the distance.
The main issue is resistance (R) per foot. Here's the difference, per foot, at 72 degrees:
10: 0.00102 Ohms / foot
12: 0.00162 Ohms / foot
14: 0.00258 Ohms / foot
So running a 30' 10 gauge wire would be:
30 x 2 x 0.00102 = 0.0612 Ohms
Now, for the 6' of 12 gauge you want to run between the wall and your amp:
6 x 2 x 0.00162 = 0.0194
So the 6' of power cord is 1/3rd of the entire resistance.
PS - We use 2x the distance because both the hot and neutral count.