I already had the amplifier and sub from a prior install, and in that install I had discovered a problem with the pairing. The sub is an Infinity Kapa perfect 12 VQ rated at 400w RMS and the amplifier is an Alpine MRV-420 rated at 350W RMS. Driving the sub at high voltage, with line levels in excess of 4v and the gains maxed out means that the amp is producing closer to 450W RMS and the sub, which is well regarded as being able to handle much higher loads than 400W RMS, just laps it up, but had one small issue that needed sorting. It would overheat during extended sessions of Drum and Bass at full power! To sort this issue, I stripped the amp back to bare metal, rebuilt it using high grade CPU heat sink paste and added a temperature controlled cooling system utilising 6 x 40mm fans in a push/pull config. Needless to say, it can run at full power and then some, all day long now !
These images are of the strip & rebuild: