MEZZA22:
I don't know where the Dynaudio amp is fitted, but the Pioneer sub-woofer is a perfect fit, and I do mean perfect, under the passanger seat. Fits perfectly between the seat rails and right up to the seat edge even when the seat is as far back as possible. The floor under the seat has a ridge half-way down and the sub-woofer fits right up to this. It is as if it was designed for the Golf! What luck!
PS: My sub is not bolted to the floor but is very secure using velcro as the company did not want to do any drilling.