Anyone using a sub with Merlin VSM Milleniums?

Yes, you do use the BAM with a sub. Find a woofer system that crosses over at 30 Hz at 12 or 24 dB per octave. If you use a 24 dB slope, you must invert phase on the woofers.
One of the most important aspects of the BAM is that it optimises the response of the VSM down to the lower resonant frequency of the woofer (which no sub could ever do). This allows a flawless transition into the sub frequencies and then the steep filter in the BAM removes the potential for overlap of output at the crossover region. Without the BAM in a sub woofered system, central and upper bass would lose resolution and integrity. In fact, over 90% of the people that have heard the VSM BAM combo prefer it to a sub woofer with the VSM without the BAM.
Bobby@merlin

i used to use stereo subs w/ my milleniums: entec LF-20s, placed slightly in front of the VSMs to time align them. bamm was taken out, and i put a passive x-over (much like those found on audioc.com) in line w/ the amp to roll the VSMs off at 100hz, with the subs running full range. i had to decouple the subs from the floor to reduce a bloatiness in the bass.

with all that, i had it REALLY close. indistinguishable almost from the merlins w/ the BAMM in place. result was a lot more impact down low and a much bigger stage per the 20hz area info.

ultimately i sold them, when push came to shove. i got tired of having all the boxes, and when given the opportunity to buy a world class digital setup for the $$ i got for the entecs.

i think there's probably a few good subs out there that would work --- none of them fire downward BTW. i cannot stress the importance of that point enough.

best
rhyno