Higher Efficiency Speakers


I am going to start my quest for speakers. My room is 13.5x13.5 but open on two sides... so not an ideal space. But never the less this is what I have to deal with.  I have a set of Vandersteen 2ce Sig ii but would like to upgrade. Was thinking about something horn. But seems when you go that route it gets way out of my price range.  Thought maybe look around for some Used Vandersteen Quattro CT but budget starts to stretch at that point. Like to stay under $10,000. What would be good speakers to look for to demo? If my room was alittle bigger.  I’d almost go the other way, and look at Small Maggie’s and Monostrap my amps.
System
Atma-sphere M60
Atma-sphere UV-1 ( Probably the most Modded. Will be at the end of the month. Lol) 
Bel Canto Dac

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I have my Vandy Treo's at near mid-room (between LR and DR 12x24x8).
I have excellent soundstage and reproduction with a pair of 2wq subs.
I owned the 3a sigs and went up to the Treo's. No comparison, everything is much more coherent/ seamless.
I also own Ralph's MA-1's/MP-3, as well as Ayre MX-R's.
Both amps are beyond what I thought I could imagine/afford.
I would ask Ralph is the M-60's could power Treo's-If you got the 2wq subs, I think it might work. And, you'd be 85-90% close to a Quatro.
Bob
Wow. Maggies, Devores. Spatials... you can't go wrong with any of them! Still, something not too large.

Maybe the Spatial M3 TriodeMaster - 93db @12 ohms.
Ihasa, OTL amps are High Current so different from regular tube amps. I could Monostrap my Atma-Spheres and get about 180 watts into a stable 2 ohm load and have High Current. Tubes would last as they’d never be stressed. Think that would be awesome... but gets pricey even buying used.... okay back to reality.... lol... 
 
Treos maybe tough to drive with the M60’s. 85 dB at 6 ohms. Also, at that price with the subs. I am closing in on the Quattro CT.... 87 DB at 8 ohm... which is the treo with the Subs built in... Ummmmm, so many decisions... 

I am doing a similar search. Take a look at Audio Note AN-E. Large range of prices. Maybe problematic for your room due to the fact that they prefer to be placed in corners.