The Voxativ 9.87's come bundled with the Voxativ dipole bass units, which are absolutely remarkable: dual high efficiency 98dB sensitivity drivers facing each other, driven by a 250W class A/B amp. By far the cleanest and fastest and most musical bass I've ever heard. If you need a sub for any musical system (Voxativ or no), you must give these a listen.
When I was running my Omega Super Alnico Monitors, I experimented pairing with my JL Audio F112v2 sub, but I didn't find it strictly necessary. The Omega SAMs very comfortably get to the mid 30's. The sub was wonderful for filling out the resonances from various instruments (piano, strings, etc) and you definitely heard a richer, more full sound, but the SAMs by themselves were very satisfying for me.
The Omega Compact Alnico Monitors were a bit thinner, giving up maybe 5-7Hz on the low end. I found that I really wanted some additional heft at the low end when listening to the CAMs.
As an interesting aside, my buddy recently snagged a First Watt F1 amp
http://www.firstwatt.com/f1.html . This is a 10WPC class A current amp, that in theory is more immune to variable impedance loads from the driver. In theory, it is very well matched to single driver units like the Omegas.
The combination of the F1 with the Omega SAMs blew us away. To give you a sense of the moment, within 5 seconds, people were exclaiming WOW! and my buddy had his arms in the air yelling "Yes!"
They sound like full range speakers now(!), with bass clearly audible into the mid 20s (although diminished) with even more incredible dynamics and rich full presence (usually a weakness of the Omegas). Absolutely no sub required with the SAMs if you have this amp! The F1 is powering through any load quirks from the Omega drivers and taking names!
As context, I have also driven the SAMs with a Classe CT-2300 amp (300WPC) and Benchmark AHB2 amp (100WPC) that were normally connected to my (dearly departed) B&W802d3 speakers. Using those more traditional amps, Omega SAMs sounded like OK bookshelf speakers. Absolutely nothing like revelation we heard with the F1!
He's loaning it to me for the weekend, so I'll be playing with it with my Omega SAMs and Voxativs and BluDAVE, to get a better sense of the tradeoffs between transparency and imaging (from having an amp in the chain) and dynamics and range (from having a kick ass current amp in the chain)