One could run them in series or in series with a series network between them that will allow only the top woofer to cross to the tweeter. This would not give you higher sensitivity or deeper bass. It would give you lower distortion in the lower ranges.
Now a pair of M-130/16's in parallel in an MTM arrangement with the woofers loaded in a transmission line and I think you'll really have something.
Do you think the improvement from the extra m-165x in series would justify the cost of the extra driver? If moving to the 2nd suggestion there, do you lose performance with m-130's vs. the m-165, and in what way? I don't know a ton about transmission lines, but it sounds like a decidedly different type of speaker than the original 2x design. Would any of those changes even matter if considering making it three-way with a servo sub? I ask those things all at once because they're indirectly hitting on the same questoin: If I add the sub, how well will the rest of the design carry down to the ranges the sub will take care of, and is it as coherent as the original design all by itself.
I currently have my mfw-15 crossed over from my rs450's at 80hz, and if I go any lower, the midbass seems to thin out badly and the sound just won't blend well. With it crossed over at 80hz, however, I not only have some room problems that make the bass pretty hit or miss throughout the room, but it's just not as controlled as I really want it in the 60-80hz range for music listening. I want something that plays strong enough down into the mid 30's that I can cross over to the mfw-15 at 40hz (lowest my reciever will do it) and get a nice smooth response with great dynamics and extension. I know I don't need to go into the teens on lfe for music, but this is a multipurpose system, and I like the sound/performance of the big mfw at the bottom end. It goes low enough in-room to suck the air out of your lungs and make you nauseous.
The neo 2x design appeals to me because I've always loved the sound of planar/ribbon tweeters, I've heard a number of your designs and have really liked them, and because I'm not sure OB is my cup of tea so the OB-X series is out. I heard x-statiks and found their holographic qualities to be interesting for moves, but not good for the dialog as it wasn't anchored to the screen very well, and for music they just felt a little vague. Anyhow, I'm considering ways to do a slightly souped up version of the floorstanding variation. A simple, sealed, 3-way neo-2x w/ servo sub might be all I could ever want, but it seems like a lot more capability down low than the everything else and I'd like to find a way to add a "little something" without complicating the crossover network tremendously, or moving completely away from your design. On the other hand, maybe the integration would be better with the tuning flexibility a ported design gives. As you mentioned less distortion with a second woofer I'm thinking maybe that translates into better dyanamics, which is one of my favorite things my rockets do well. I also love the attack of the vifa ring radiators but find they get a little sibilant on some material. I'm hoping to actually audition a standard pair of neo-2x's at some point so I can get a better idea of what exactly I want from any tweaks.
Aack! Can't post without rambling!!
I appreciate any input or advice you may have
