Sound Stage and Imaging

I missed where you live but Gene Rubin lets potential buyers audition Harbeths in the LA area,

We carried Beveridge, Quad, Soundlab, Acoustat, and Apogee…. and more…. 

it was a golden time….

I have a pair of apogee duetta 2 speakers, and a pair of Polk audio SDA 2a speakers, and the polks have a bigger soundstage than the apogees, but not by much. If I were you I would look for an upgraded pair of Polk sda 2.3tl speakers. The polks can be placed right up against the wall that's behind them.

  Based on some recent posts regarding sound stage and imaging many Audiogon members have wildly different ideas when defining sound stage and imaging. I recommend you look into used open baffle speakers. I’ve owned a variety of speakers including Von Schweikert, ,Zu, Tannoy, Klipsch, Genelec, JBL and Snell. None of them come close to competing with open baffle.
  You’ve got a large room which is great for a high efficiency open baffle speaker. You won’t need to worry about acoustic treatment but they do require space from the walls. Check out the reviews of the Lii audio speakers. You could build your own baffles and be very happy! 

Even so the (main system) room is huge, the floorplan for the listening area ("room") is not that large (20x20, one side, one back wall). The speakers are located at a 'half' or '3/4' wall, and can only be 2 feet away from that wall). 

https://drive.google.com/file/d/1yRozuEvtpBvvnY4mXcfs0tSG6KmfDYo5/view?usp=sharing

Open baffle speakers: sounds intriguing. Curious: will open baffle speaker with 'normal' subwoofer kill the benefits? Need to look for an opportunity to listen to an open baffle. Might be the effect I remember when I first heard a large transmission line woofer (very natural, deep, airy; I was blown away).