Do No Harm ... well the least harm anyway

Well, there you have it. It seems I have about a snowball's chance in Hell of getting this idea to sound correct. I think I will let the Nefes play full range and let the subs give a helping hand under 50 Hz or so. My subs have all kinds of adjustments, so I can mess with them and not really worry about the critical integration of 2 different drivers at the 100Hz range. Thank you ALL!!

OK, thanks all. My reasoning for wanting to do this is to limit cone movement of the 2 full range drivers. Since they have no crossovers at all, they must play the delicate midrange as well as the thumpy bass. I figure if I can cut out the cone movement of the bass, the mids won't be smeared by that back and forth motion. I do use subs (Velodyne DD15's) next to each speaker. Since the main speakers are away from any walls their bass is not as strong as in a conventional room. My listening room is large as it encompasses the living room, dining room, kitchen and den all in an open floor plan. I have the subs lowpass set to 55Hz.

Yes, I also realize, the other option is to leave it alone. I'm just not sure if it's better to go down this path, or not.

@mitch2

Your post reads like you are happy with the passive filter, but you say it did not improve the sound. Please elaborate if you prefer the Marchand or not, and is that why you are selling it on USAM? I'm not trying to be a smarta$$. Thanks.

@mashif

Good to know. What is the slope and lowpass frequency on your sub? Also, did you lose any of the "magic" with the Marchand? Specifically fine details, depth and imaging.

Bomer:

I had the DBX Venue 360 in the system, but found it to be annoying having to run it through my computer. It was supposed to run on an iPad also, but they never fixed the problem that arose when Apple changed their OS a while back. I also did not like the additional A-D and D-A that had to be incorporated. I have been considering the Mini DSP Studio, or the Marchand passive crossover, but after a bunch or reading it seems this whole idea is a can of worms that I would probably have wished I never opened.

My 2 subs are VINO (Velodyne in name only) because, being Velodyne, they have both broken. Tired of repairing them, I bypassed the electronics and ran wires to just the drivers. So now they are 15" passive subs. I use a Crown 2500 for the lowpass (55Hz) and all is working fine. When I said "thumpy bass" I meant that in a good way. Like the sound from a kick drum, those frequencies are best suited to subs, not to a full-range driver. My preamp has 2 outputs (XLR and RCA) so the XLR goes to my Benchmark amp and the RCA to the Crown. Interestingly I have found that hooking the subs out of phase produces more bass than in phase. Even though the subs are close to the main speakers. Perhaps the Crown amp inverts phase, but I don't know. Everything sounds pretty nice right now, but as a hobbyist, I am always thinking of something to change.

Yes, The XM-66 is probably the highest on my list of possibilities.