Need some Amp help - a little new to properly powering speakers

@willemj , I think you might be confusing sensitivity with efficiency. They are not the same; the latter is based on power and ignores impedance, the former is based on voltage and impedance thus matters quite a lot!

Now if you are driving a larger room, you will need serious power regardless. If that is the case, you might consider a set of Sound Labs, as they are better at playing the higher sound pressure levels you might need in a larger room.

You do not need more efficient speakers for more detail. The most detailed speakers may well be Quad electrostats, and they are horribly ineffcient.

The first statement is true, the second is partially false. Quads are planar loudspeakers, and so the 1 meter measurement does not give their true efficiency. In general you can add 6 db to the measured figure and be a lot closer to their actual efficiency. This is true with any planar. 

Al, If a tube amp were used on this speaker, it would probably do fine if used on the 4 ohm tap and if also running about 20 db of feedback. The impedance curve would then present no worries.

I only mentioned a tube amps simply because the OP is dealing with a lower volume loss of detail. Low level detail is something that tubes can do considerably better than transistors. IMO this has to do with the linearity of the devices themselves; even pentodes are not that bad at lower power levels.

I notice at lower volumes a lot of the imaging and clarity disappears.

That's a problem with the Yamaha. Going to higher power won't help it.

There is this thing called the 'first watt', which is the idea that the first watt of power is the most important. Apparently the Yamaha isn't doing that bit fairly well. I suspect if you look at its specs, at lower power levels the distortion might be quite a bit higher than at higher levels.

Better quality amplification is better at that problem. If you go with tube gear, even better...