I originally started with a Marantz SR5400 receiver with 90watts rms per channel. I had it connected to all of my speakers. The only ones I will discuss at this time are the mains, Paradigm Studio 100 V3. They sounded quite good when powered with the Marantz. Later, I had purchased a Rotel RMB-1075 5-ch amplifier with 120watts rms per channel and a Rotel RB-1090 2-ch amplifier with 400watts rms per channel.
After purchasing the Rotels, I had connected the Paradigms to the RMB-1075. Basically it sounded about the same as when connected to just the Marantz. 30watts really won't gain you much additional volume. Sound stage and all that stuff was same as well.
However, I did notice a difference when the Paradigms were connected to the RM-1090, which is how I currently have them configured. The main difference is I can reach a louder maximum volume. I don't have measurements to show the difference. There wasn't really any change in the sound stage and all that stuff, but you could kinda say the sound was perceived to be more full. I think this is only due to being more dB's, especially on the lower frequencies. As mentioned earlier, at matched sound levels, all three methods of amplification sounded the same.
Basically what I am saying is that separate amplifiers can allow for the opportunity of more power to the speakers and independent processor updatability, but the sound stage and stuff still comes from the device doing the processing and your speaker placement. I do plan to upgrade to a separate processor and omit the receiver. My reason for doing this is so I only need to upgrade processors in the future. The amplifiers should continue to do their thing no matter what processor I have in the future.
Keep in mind, if you look at a speaker's sensitivity rating, for instance 88dB/watt at 1 meter, this means you might get roughly 88dB of sound at 1 meter of distance with only 1 watt of power. Also, you gain roughly 3dB of volume with every doubling of the power. 3dB more is typically known as just noticeable difference in volume, and 10dB more is twice as loud. You can google this stuff to learn more, but one such link is: Power and dB
1/8w gives ~79dB
0.25w gives ~82dB
0.5w gives ~85dB
1w gives ~88dB
2w --> ~91dB
4w --> ~94dB
8w --> ~97dB
16w --> ~100dB
32w --> ~103dB
64w --> ~106dB
128w --> ~109dB
256w --> ~112dB
512w --> ~115dB
All numbers are approximate and only there to show the relative relationship between amplifier power ratings and SPL. Also, most of us sit farther than 1meter from our speakers, so these numbers are less (as shown in the link I posted above) in your listening position.
Hope this helps. Also, everyone, feel free to correct me if you see an error.