Which speakers will fill 5,000 cubic ft coherently

I can't recall if you mentioned the distance from the rear wall to your speakers, but if it's close then then Definitions might not be the best choice since their woofers are rear firing. Might be boomy.

My Definitions were 12 inches from the rear wall with no boom, no problem. However, I would still recommend the Presence for your situation. Black hardware is available and your wife can choose any color on earth. My speakers are the color of new copper tubing. Glossy and metallic, they look like old fashioned radios with their woofer lenses showing slivers of dark grill cloth. Flat paint is also available so you can match them to your sofa or your Navajo rug. Be creative.

When I design a loudspeaker I try my best to keep above 8ohms and near stable. 16ohms even better. But many tubes amps will do fine into 4ohms just depends on design, transformers etc. Still best to shoot for 16ohms or at least 8 ohms if you want to run tube amps. For OTL -SET best to match loudspeaker carefully. Some of the better systems I have heard used costly OTLs wont mention from who:) But I have also heard the same basic system with diferant loudspeakers that wasent so hot at all. This is true for most all systems best to match up gear designed to work together. See many wanting to use 4ohm 88db bookshelfs or other hard to drive loudspeakers with SETs or OTL. Many post asking. I can see why they are not so thrilled if they try these amps. Kind of like shooting yourself in the foot or pissin in the wind....Your not going to like the results but its your fault not the systems..

My Definitions are close to the rear wall with no problems. I have not hear the Zu Presence or the other speakers that you are considering. The metal on the Zu speakers (Def and Presence) can be anodized black; and the cabinets can be painted any color - matte or gloss. Personally, I like the gloss black with the aluminum driver trim (it is not chrome, btw); for the record, Architectural Digest agreed. However, if your wife wants wood veneer, then Zus will not work.

Infinity Kappa 9 will sound great in that room, and they are beautiful too. But, they will need to be bi-amped.