Well there are lots of speakers but new speakers in that price range that can do deep bass will most likely have lots of compromises in other areas. I would buy used.
An often over looked speaker line for there bass is Thiel. There is a pair of Thiel CS7.2 for $6500.
Fallowing quote is from Soundstage!
"The CS7.2s bass
depth and authority are shattering, and its bass weight is wholly
realistic not warmed up to create a sense of fullness or heft from
recordings that dont have it by nature. Bass notes are carved
out with exceptional clarity, even at the speakers very depths.
Claims of 20Hz bass are common today, but if the CS7.2s 25Hz
low-end specification is correct, many speaker companies are exaggerating. From my experience, you have to pay several times the CS7.2s price to rival its deep, linear bass."Stereophile
"Thiel speakers are known for excellent bass, but the CS7.2 was even better than I'd expected. From the mid-20Hz range on up, it was fast, clean, powerful, and very naturalin other words, dead on. Detail was excellent, as was the recovery of ambience and spatial cues. On "Saturn," from the Zubin Mehta/ LSO reading of Holst's The Planets (London/Classic CSCD 6734), I could clearly hear the individual double basses lined up at an angle. The walls beside and behind them were solidly located, and there was a great sense of the space between the instruments and the walls.
Fast, melodic bass linesRay Brown's Soular Energy (Concord Jazz CCD-4268), for examplewere sweet, clean, and bouncy. But what really struck me was the 7.2's reproduction of bass drums, and the breathtaking drive and impact that it added to orchestral pieces. My notes on the second movement of the Reiner/Chicago performance of Prokofiev's Lt. Kijé (Chesky RC10) say it all: "Wowincredibly realistic, with a fast initial transient followed by a seismic, blooming weight . . . all the while maintaining a clear pitch, harmonic structure, and distinct skin tone. Fantastic! I've never heard bass drums like this outside of a concert hall."
The only nit I'll pick is that the 7.2 slightly emphasized the very lowest bass relative to the upper bass and lower midrange. This didn't come across as an imbalance or discontinuity, however, but as if Ray Brown just wasn't playing quite as loudly at the top of his range as at the bottom."
I am really looking forward to the CS7.3 that is coming out down the road...