Do you think you need a subwoofer?

I lived with the Thiel CS6s for about a year (Krell 400cx/KCT amp/pre)and found that there were times when I wanted to have that last bit of extension. The CS6s are rated down 3dB at 27 Hz. Almost a year ago I ordered Thiel's SS2 sub with the passive crossover and after setting it up and letting thelectonics settle in, the soundstage opened up on all recordings. The sub does not make itself known, but in addition to the wider stage, whenever there are footfalls in a "live" recording (Cowboy Junkies) is a good example, I can now hear and feel them as if they were present in the room. On Saint Saens Organ Symphony the low pedals energize the room solidly, but again only when called for. As I said, the sub is audibly transparent with the CS6s, just there when it is needed, in fact when I turn it off and just listen to the mains alone, there isn't much apparent difference in extension of the bass, but the soundateg is smaller and those last few Hz are not there at the tactile level. I think the main challenge is to take the time to fine tune the sub so that it is "not heard" and just picks up where your mains leave off.

The reasons for a sub with monitors is obvious. More and better bass, when they are integrated properly.

For "full range speakers" which only start to roll off at 32hz or below, unless you want to hear airplances taking off in home theater applications, or are an organ nut, I believe that the best use of a sub is when your full range systems create bass problems in your room because the location of the main speakers creates very uneven bass response. You can roll off the bass at a ligher level and put the sub in a location that doesn't exacerbate the problems inherent in the room size.

The problem with using a sub with any "fast speaker" is proper integration. This is especially so for speakers with little inherrent bass, say those that are down 3 db at 60 to 100 hz. This requires a sub that is equally fast in the overlapping frequencies. Very hard to find, especially with panels and electrostats.

Life is a trade off. :-)

As full integration of subwoofers is quite difficult and because most subwoofers cannot keep up with many midrange drivers and tweeters, I would seek to avoid them. But because these same problems bedevil full range speaker designers, there is no easy advice to give.

For a long time I had Beauhorns with a single driver. They were great from about 65 Hz to 13k Hz. I finally found subwoofers and an amp that would keep up with them using a high pass filter on the subwoofer amp starting at 40 Hz and the natural roll-off of the Beauhorns. It looked good on instruments and was satisfying, but when I got the Acapella LaCampenellas, I realized that there was much missing from about 125 Hz to 50 Hz. But with the Acapellas I don't have house shaking frequencies below about 28 Hz.

So the answer to your question is both absolutely you need subwoofers and absolutely no subwoofers are impossible.