I've resisted using a subwoofer (or really a woofer based system, not really a "subwoofer" per se) with my Sound Lab 845PX speakers for several years. The reasons for my recalcitrance are as follows:
(1) I've never met an electronic crossover that did not color the sound in some objectionable and noticeable way.
(2) I am getting tremendous low bass response from my 845PXs with no added woofer (but see below).
(3) I ascribe to the idea that one-way systems are a virtue; I have revised the electronics in my 845PXs to eliminate the filtering that precedes the two audio step-up transformers. (This is another long story not suitable to this thread.) There is no crossover in my system anywhere and only one 0.1uF capacitor in the signal path, from the line level input of the preamplifier to the speakers.
(4) I envisioned that adding a woofer system would require introducing at least two large-ish and probably ugly cabinets into our living room, and I am or was loathe to do that. Esthetics matter to me.
However, the price I pay for this policy is in fact that I have too much bass. I do perceive suboptimal resolution and definition at the extreme lowest frequencies, where there is not so much a "peak" but a gradual rise in speaker output. I use Tube Traps behind each SL panel to ameliorate this problem, but it is not a perfect solution. I believe this is because the SL speakers rise in impedance as frequency goes down. (I've measured this.) Since I use OTL tube amplifiers, this results in a broad rise in speaker output, inversely related to frequency. (The OTLs love high impedance.) Lately, I perceive there are ways to overcome my reservations about electronic crossovers, either by using only a capacitor at the amplifier input, to roll off the 845PXs at low frequency, or by using any of a very few electronic crossovers that may be acceptable to me. In addition, one of you guys pointed out that a pair of woofers could be placed behind the panels, out of sight, and that the cabinets need not be huge.
Over the years, I have made this system better and better. Now I think the only thing left is to take a shot at adding a woofer supplement. Duke LeJeune probably knows more about supplementing SL speakers than anyone, and I intend to consult with Duke on the best course of action.