if a SVC sub is rated at 4ohms would it proform better with a 4ohm signal from the amp rather than running 2 subs in parallel to gain a 2ohm signal from the amp, i know that 2 4ohm subs in parallel make a 2ohm load on the amp so each sub still gets roughly the same watts RMS as having 1 at 4ohms but would the SQ or SPL suffer by running a 4ohm speaker at 2ohms?
There is a little more distortion when the amp is running a 2 ohm load, but it is WAY less than you would audibly notice. It's only about .5% more, you won't usually notice anything less than 10% in a car anyway. In short, nothing will suffer. I usually stick to one amp, anyway. Running two you can possibly have differences between the two amps, one amp will guarantee that the power is distributed equally.