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 - There is nothing wrong with Paradigm Studio/60. I had the same speakers v.2 It performed decent with integrated Cambridge amp but got much better at low volume with class D Icepower amp (Rowland 102). I found later review where they mentioned good performance of Icepower at low levels. Now I use different speakers (Hyperion 938) but low volume sound is still very good (lows, highs, clarity, dynamics, imaging). Actually, imaging is better at low volume. I have too much reverberation in my room and at low volume I get less audible reflections (echo dies faster). At high volume room brightens the sound a little more than it normally would be. Hyperion speakers are exceptional!!!
You are hearing the effects of the additional amperage the bigger amp is providing. Most speakers like to be connected to a high-current amp....