You want killer bass, with no big speakers on your desk....
It's entirely possible I don't understand your application. If it's the typical approach of desktop speakers, music, gaming, videos etc., then full-range mains would serve you best.
The Behringers would have plenty down low for you, whatever sub you're considering, very likely
couldn't outperform the Behr's two 9" drivers in a ported cabinets. Plus, the discontinuity
of a 3 piece sub/sat rig near-field is significant. You're certainly welcome to do as you wish, however these suggestions are not arrived at merely off the cuff. I'm certainly not the brightest AVS'r around, but I do have decades in and around audio both professionally and at home. And with regard to desktop audio,... been there done that
, .... the 2.1 subs are largely garbage. Even the one's that truly excel (never seen a really good one, but there out there), it would be nearly impossible to integrate them properly to achieve anything close to what one could easily get with normal two channel full-range speakers due to the application distance.
Here, is the frequency response of a Klipsch Pro Media 2.1 system at normal near-field conditions for desktop application.
Notice the total lack of any output squarely in the heart of the impact range, additionally, the unacceptable ragged response,....which is even more unbelievable because near-field response should be much smoother than this. I took distortion measurements of the sub as well and they were the highest levels of THD I've ever seen.
Oftentimes individuals utilize a 2.1 sub sat combo with desktop computers. I've had many sets myself. However, once one experiences normal desktop usage with high resolution, wide-bandwidth response, that possesses a coherent presentation top to bottom, they'll never go back to the typical BS that is the 3 piece computer genre of speakers.