Subwoofers

I have a single Depth, and find it to be the best I've used
with my (electrostatic) CLSs, for the following reasons:

Incredibly fast transients, which you'd better have if using a sub with electrostatics (better than the Descent IMO)

Very tolerant of placement (probably due to the omnidirectional radiating pattern, but that's just a guess on my part.) Very hard to hear where they are (a good thing) so two are really not required, unless for HT effects I suppose.

Very easy to dial-in to your room and main speakers.

My experience with other makes: Velodyne (really suck!), Hsu (OK budget sub for HT), Kinergetics towers for the CLS (hated them, but they looked good!) Wilson Puppy 2s (incredible as subs, but required electonic crossover and another stereo amp -- too much stuff)

Have no listening knowledge of the Vandy or Rel, but am aware of their good reputations, so they'd be worth comparing. What attracted me to the Logans was the innovative solution to eliminating cabinet resonances, and the uniform radiating pattern. Also, FWIW, I've never heard a downfiring sub that I liked.

Goatwuss, the ML Depth has (the important low pass) x-over points at 30, 35, 45, 55, 65, and 80 Hz (a total of 6, not 2)

If you are concerned about using high pass filters (40 and 70 Hz for the Depth) I'm curious why that would be important to you. Most folks interested in good sonics use a separate set of interconnects for the sub and don't pass the main audio signal through it. Besides, why would you want to castrate the low end of the main speakers (especially Dynaudios!), since the purpose of a sub is to augment and extend the low end response of the main speakers, not to replace it.

The ML Depth also has a full complement of other adjustments necessary for good sub setup: 4 phase angles, level adjust, plus separate 25Hz level adjust (very useful) as well as separate LFE input for an HT processor which bypasses the subs own settings.

Providing additional functionality for creating sonic environments, adjusting equalization for problem sources, etc. should be done through the (HT) processor IMO, not the sub. Getting those functions by directly altering the sub's response means that the driver-enclosure design can never really be optimal across all functions.

I agree with you that adjusting for room response and finding proper placement is quite important, but if you can't achieve good results using the 25Hz level and phase angle adjustments on most subs, then you need to treat the room, which most people agree is primary source of bass response problems.

One of the best ways (as described in some other threads) to set up a single sub (a bit harder to do with two subs) is to place the sub at your listening position and then walk around the room to find the spot(s) where the bass response is flattest. Then locate the sub at one of those places.