Can someone give me an explaination re: power amp.


So, I own a simaudio i-5 driving paradigm studio 60 v.3, and I am not happy with the sound at low volume. turn it up everything is great, but low volume has muffled sound. Everyone says the paradigms are efficient, but i go out looking for more efficient speakers, and happen to come home with a loaner power amp- a simaudio w-3 (125 wpc), and the sound at low volume sounds markedly better with the power amp. this is contrary to everything i have convinced myself to believe. i have convinced myself that a good integrated is all i need, but I cannot deny the sound. so instead of asking the age old separates vs. integrated question, i'm just going to ask- why does my system sound so much better at LOW volume with the power amp. Maybe the speakers aren't as efficient as I thought? Maybe the 70 wpc simaudio i-5 isn't as great a machine as i thought? maybe there's a technical explaination? Please enlighten me! and thanks, and merry christmas to all you audiophiles out there! (oh, and the reason I didn't come home with speakers is that i really love the full range of sound from the towers, and i couldn't find any highly efficient speaker that had the range I enjoy. not that it dosen't exist, but i just couldn't find it. I live in portland, oregon).
blazerfan
ball parked the volume issue, but feel that I over compensated (turned the volume way up) when listening to the integrated, and still experienced better sound with the w-3. with everything i know about high power and/or high current i agree they do not offer a rational explaination. however, there may be things I don't know about high power/high current that may lead to a rational explaination. this is what i'm trying to find out.
Blazerfan - Twice softer means 1/10 of the power. Four times softer means 1/100 of the power. At low sound levels power might be in fraction of a watt. Amplifiers' distortions, damping factor, bandwidth etc. are measured at relatively high level. Amp (and speaker) performance in not so good at very low levels. High performance amp might have enough of "reserves" to sound good very soft. At medium levels both amps might sound very close. At very high levels higher quality amp will outperform again.
Your w-3 amp has 0.02% THD at 1W. At a fraction of a watt it might have 0.1% - still not audible while amp with 0.05% THD at 1W might have 0.25% THD at the same fraction of a watt and it might become audible.
I've never understood why so many regard the efficiency of a speaker as a virtue. The most accurate and best sounding speakers I have heard have also tended to be the least efficient. Take sealed/infinite baffle speakers for example - you have to crank them way up to get much volume, but when you do the sound is effortless and natural. In contrast highly efficient speakers tend to sound more compressed, out of control, and have less nuance in their dynamics, both at high and low volumes. Who is pushing this notion that efficiency in speakers is a virtue in itself?