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

Moskaudio (OP) didn’t say the Rotel played louder. What was  pointed out is that the Rotel played at lower volume levels was "clearer"`(and better bass) sounding than the Yamaha at similar lower volume. This would suggest that the intelligibility was improved with the Rotel driving the same Polk speaker. This indicates the Polk is capable of better low volume performance when a better amplifier was substituted.

The Polk wasn’t the limiting factor, it was the Yamaha and its limitations. Can you improve beyond the Polk speakers? Yes you can, you can also go further in quality than the Rotel amplifier as well. Some people downplay the importance of high quality amplification and this is an error. Speaker quality matters no doubt but the same can be said for quality power amplifiers. [ can recall experiences where merely changing only the power amplifier resulted in substantial sound quality improvement. 
Charles

Moskaudio
Atmasphere mentioned tube amplifiers in his reply to you. You Polk is rated at 88 db sensitivity and an 8 ohm load. It would be very informative to listen to your speakers driven by a good quality push pull tube amplifier of suitable power. You may find they have more to offer  than you're currently experiencing with the solid state receivers, 
Charles 

@kosst,

The OP stated that it "sounded much clearer at lower levels." He did not say it played "louder."

The fact of the matter is that a fair comparison of amplifiers requires matched levels.

High efficiency speakers manage greater low-level dynamics for a given volume.  His original post stated that he noticed a lot of "imaging" loss at lower levels. Maybe he was referring to imaging in the true sense of the word, but I'm betting that dynamics is the more appropriate adjective. I've never had an issue with low-level imaging, but all mid-efficiency speakers I've owned struggled to produce decent dynamics under 70db, regardless of the paired amp.

 I know...I know...you'll tell me I've never owned any decent speakers and that I apparently haven't heard the Focal Arias...

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 Harbeth range is also very detailed, at both high and lowe levels, and they are not particularly efficient either. All that such speakers need is power, and the more the better.