A sub will add more weight to the P3ESR. I can't think of any reason not to use one. I have mine set up in a nearfield system, about 3 1/2 feet from my listening position. I use a SVS SB12 NSD.
How big is your room? That should dictate which sub(s) (multiples are better if you have the space) to look at.
How big is your room? That should dictate which sub(s) (multiples are better if you have the space) to look at.