Sub users...

Rives summed it up well...I also use 2 subs to even out the modes and to enhance low end weight and impact below 30hz which is where my Sophias begin to roll off:O)

Bass frequencies are sent to both channels in 99.9% of mixes. Below around 100 Hz you cannot tell where a sub is anyway (if you can it is because leakage of higher frequencies - you can use a steeper filter in the case of a poor quality distorting sub). Your fear is really unwarrented if you intend to get a high quality subwoofer and correctly match it with your mains.

If you buy a ported boom box of a subwoofer then it will indeed ruin Dave Brubeck but not because drums will jump around but mainly because of masking from all the bass resonance and poor transient response from a cheap sub. The most expensive driver on large mains is usually the big woofer. The hardest and most energy demanding driver on any speaker is the woofer and the LF. Logically you might expect to pay as much (or more) for a subwoofer as your mains in order to maintain a similar level of quality.

Thank you all for the great replies. While I have not researched subs, the JL Audio F113 is the one that has my attention. I would be using it to augment the lowest notes as you hint Rives, 30hz'ish and below.

I use a pair of Vandersteen 2Wq subs. Since these are fed from the amplifier speaker taps, they are indeed stereo subs. I have them positioned behind and outside the mains. I have no issues with imaging of low frequencies - images are stable in the range covered by the V2qs.

Did you consider a Wilson Watch Dog? Your speakers have a Q resonance bump around 80 Hz - you can see this on Soundstage measurement plots. This probably affects group delay also and the way the speaker integrates in the room. (speaker may resonate after the music stops up to an extra cycle or so due to this "tuning")

I have no experience adjusting to this speaker but it may be important to match this resonance to get smooth integration. For example, an SVS PB13 Ultra has three ports which you can block or unblock in order to adjust Q resonance (will affect group delay) and this might allow more seamless integration (you get four options of resonance and group delay by blocking none, 1, 2, or all three ports)

Perceptively, lower group delay will give a tighter bass sound kind of like a traditional Basie jazz drum set (just a hint of kick through room pressure). Higher group delay will give you a fuller rock kick drum sound in the bass.