Sound Stage and Imaging

As mentioned, my single sub is 18". Don't want to trust it to handle 100 Hz (and the Nautilus are not known to be 'weak down low'.

But I have to go high in my small setup with various small bookshelf speakers, some of them do NOT feel good handling 80 or lower (certainly not at higher SPL), so there i need to drive the DD15 sub to 100 Hz. 

@riccitone 

A second sub will do a whole lot. The only limitation on subwoofer size and numbers is the room you have for them. There are excellent drivers available today that can operate in very small enclosures, you just need more power. I advise against open baffle subwoofers. I tried that approach as I have been using open baffle speakers (ESLs) since 1978-9. The thought was that it would match them better. It was a mess. The wavelengths are too long. Subwoofers are omnidirectional and the out-of- phase waves cancel in an unpredictable pattern literally canceling out some notes. Today with digital crossovers and time alignment it is a breeze to match subs perfectly. One subwoofer is always a mistake, it is  putting your bass in prison. The minimum for a point source system is two. Open baffle speakers by all means, but not the subwoofers.

A hifi shop owner that got a fat stack from me recently knows how to make speakers sing. I used to stop in monthly and listen and he could take a pair of large floor standers and have them sound like a live band one time and the next visit, in the same room, same wall have them sound like mini monitors. I’ve heard him do it with every new feature speaker he demonstrates. 

I asked him how he does it and I get a smile back for an answer. 

@steve59 That is easy: he uses the cheap china pixeldust from Walmart at one time, and the audiophile quality $50k/pound pixeldust the other time. And uses his home made electrical current with ground rod staked into the equator at 11.11 pm on 11.11.

Try to get a pair of used Odyssey Audio Kismets. Soundstage is exactly what they do best. Wide and deep.