Higher powered but efficient amp with the imaging of a Pass XA-25?

@atmasphere Thanks! The Spatial X5 are really terrific speakers. Clayton and his crew have done a wonderful job with them. And I know they particularly shine with tube amps. But they just were not right for my situation.

One correction: the Spatial's were five feet from the front wall. And they sounded wonderful... if you sat in the very narrow window of a sweet spot. Most natural sounding tweeter I ever heard. But stand up? Lose all HF. Pour on some power? My perception is they don't scale well. And even with self-powered 12 inch woofers they didn't energize the (rather large) room as well as I like.

Mine is not a dedicated listening room. It is a combination living, dining, and kitchen at 25 x 25 x 8 feet. I have music on almost all the time, as I work in the kitchen, eat dinner, read, compute, or less often just sitting to listen. But I want to enjoy satisfying reproduction whatever I am doing. In this situation the KEF Reference is getting me closer to where I want to be, but there is still room for improvement. 

@markmuse If I were in your situation, I would first talk to Duke at Audiokinesis and get a set of his Swarm subs. They would allow you to have proper bass anywhere in the room. The Swarm is 4 subs so as to break up standing waves that otherwise cause bass nulls to appear in the room, often at the listening position. They also prevent too much bass elsewhere in the room.

That would free you up to use a smaller speaker since the Swarms are good up to about 50-60Hz. That would open up a lot of possibilities for easy to drive speakers; if they are easy to drive the amps don't have to be as powerful, and often the smaller amps are the better sounding ones.

XA25 is a great amp partly because it is a class A amplifier.

So, if you want efficiency, you have to move away from class A and also probably away from tube amps.

A best compromise may be other Pass Labs amps which are class AB.

X150.8 or X250.8 (both class AB), will come extremely close to the sound quality of the XA25, and still satisfy your your efficiency & power requirements.