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

Apparently it is the Yamaha. The OP just posted above that lower volume sound quality improved significantly when the Rotel replaced the Yamaha component. OP, I would heed the considerable knowledge/wisdom of atmasphere. He’s absolutely right in that high quality amplifiers sound very good in their "first watt" range of power. Providing more power from a lesser quality amplifier (poor first watt performance) won't solve the problem. 
Charles 

Such comparisons are only valid if the level is equal within 0.2 dB. For that you really need a volt meter.

Your speakers are of relatively low efficiency. That's the issue, not power or quality of power. As willemj pointed out, unless you level matched the Rotel and Yamaha for your comparison, it's likely the Rotel was playing at a higher volume when you perceived the improvement.

If you want low volume dynamics, you simply need speakers of high quality and greater efficiency. 

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