Which speakers will fill 5,000 cubic ft coherently

The accuton drivers are not well known for playing loud/dynamically. So it is not surprising that a two way with these drivers might struggle in a large space. To me I don't think you need to go overkill - most equivalent price range three or four ways would make you much happier, IMHO.

I am not sure you need to go overkill but if you want beauty and assurance that you will be able to fill the space then Dynaudio Temptations, Wilson Alexandrias, Evolution MM3's would all do it without a single doubt in my mind.

Springbok,

Why not try pulling those beautiful Kharma's well out into the room and away from the side walls....(while the wife is out) and see if it sounds better?

cant go much beyond 10" wide to fit in the apce between the amp Boxes and the corners.

Please Please don't tell me you are placing such awesome speakers in a corner or near a sideboard or drawer with sharp angles - this will definitely affect the soundstage and may collapse it to the speakers (edge diffraction = claustrophobic sound)

=> this might be a major part of your problem...any reflections within less than 7 msecs can severely affect the openess of the sound...the worst is that everything collapses to the speakers. My rule of thumb is a minimum of three feet from side walls but four feet or more is safest. Remember our ears sense timing for where a sound comes from....the time a signal arrives is how you interpret where it is (you have to go 10 DB SPL louder to make your brain pay attention to "loudness" rather than arrival time cues) Now when you clutter or crowd early arrivals with edge diffraction of reflections it can really mess up the size of the soundstage.

This is the most interesting thread in a while....what a conundrum of imposed constraints (amplification equipment, speaker placement, and loud unstrained sound to fill a large space, and not least of all the WAF factor). All understanable constraints but nevertheless making this problem fairly unique!

I'd suggest another option: biamping! Why not use an active filter to split the preamp signal to allow the beautiful 58 tubes to drive the midrange and tweeter of a nice dynamic three or four way. Then use a big bad boy SS amp on the woofers...and caboom - you got the smoothness and clarity you want in those tubes with the ooomph you need for a large space for blissful unstrained dynamic sound (not only will the big bad boy amp driving big woofers fill the room in mind bending accurate bass but you will ease the strain on the amplification to the mids and tweet, which can play louder and sweeter too!)

...anyway I just thought I'd toss that idea in....

Thanks for giving feedback - I would only add that it might be wise NOT to modify the SP Techs or alternatively make sure you have a kit to make them standard again...just so that you keep your resale options open and also the option to move house or change their location in your house.