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


Hello. 

 I have some polk LSIM707s that I thorough enjoy.

However, at the moment I'm powering them using a Yamaha aventage 3070 receiver which at 150 watts at 8ohms sounds pretty darn good. 

However, since these are rated at 300 watts at 8 Ohms, I assume I will need some more power. I notice at lower volumes a lot of the imaging and clarity disappears. 

I am looking at buying a 300 watt emotiva Amplifier, or a 500 watt emotiva amplifier.

I'm assuming it would be better to purchase the 500 watt per channel emotiva so the speakers won't suck it dry or stress it. 

Am i wrong in this assumption? 
moskaudio
No it is not a problem with the Yamaha but with human hearing. Louder will always sound better. Did anyone bother to look at the test results for 1 watt that I posted? Here, for data on an even cheaper Yamaha, the AS 500, the predecessor of the current AS 501 that now also has digital inputs: http://i.nextmedia.com.au/avhub/australian-hifi_reviews_2014_2014-02_yamaha_as500_amplifier_review_a...
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. 
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