Crutchfield lists a midbass-woofer from Audiofrog as being compatible.
I think it probably beats the Infinity. However, I doubt very much it's in the same class as say, Kicker, Kenwood, JL Audio, or other subs, so the question is how great the improvement is. It's a shallow-depth application, which limits things.
GS Series 8" subwoofer/mid-bass speaker with dual 2-ohm voice coils
www.crutchfield.com