Matt, welcome to Axiom. What you've apparently heard elsewhere about Axiom speakers being "bright" is no more accurate than what you've also heard about amplification. The treble response is smooth and accurate and will reflect the characteristics which are inherent in the particular source material which is being played at the moment.
As to amplification, competent design results in the sound simply being made louder without adding some inherent sonic coloration. Blind listening tests confirm that this is achieved at quite moderate cost in receivers and at somewhat higher cost in separate amplifiers when they're operated within their designed power limits. An engineer who designed a unit which had a "sound" would be subject to being fired for incompetence.
A "larger amp" has no capability to make speakers sound better at given loudness levels. If the speakers are being played at a very high loudness level(possibly damaging to hearing)which exceeds the maximum clean voltage output level of the existing amplification, an amplifier with higher maximum limits will have lower distortion, of course. In the vast majority of home listening applications typical modern receivers with rated outputs on the order of 100-150 watts are completely sufficient.
