you mean for music use? (sorry when i think stereo, i think dual subs

)
i don't think you can ask for more from the ultra, it's been tested by third parties to have very flat frequency response, very low total harmonic distortion and does not compress until very high SPL levels.
unfortunately, i don't do "musical comparisons" between subs. i'm not sure if aside from the ground plane tests and room location, if there are other "musical" aspects that are immeasurable and only heard by our ears.
when you come back to manila, let me know, you should just listen to them yourself

(i'll be in the US until the 15th though)