Alright...say you had 2 12" Kicker CompVRs wired at 4 ohms in a ported box. Would you prefer the Phoenix Gold X600.1 or the Kicker KX600.1 to power your subs?
I'd actually choose a larger amp. The KX600.1 only does 300w RMS at 4 ohms and that's at 14.4 volts. It's only 255w RMS at 12.5 volts with a 4 ohm load.
If I remember correctly, those CompVRs are rated at 400w RMS each. You would need to run the KX600.1 at 2 ohms to get close to the proper wattage, but I would still choose a bigger amp.