A good number of people have had their systems go through some kind of evolution. A common theme happens to be the transition to separate amp(s). The improvement is not necessarily the SPL levels but rather the sound is cleaner and more detailed with separate amps. With a receiver you have to share the power with preamp duties, video processing etc. This leaves a little left over for audio amplification. Using a separate amp, leaves a dedicated power supply just for audio.

Looking back, one of the most dramatic improvements was using a separate amp for all channels. I have a secondary system where I also use a separate amp (mains only). The reason was simply because it sounded more detailed using an outboard amp for the mains.

Another advantage is that one does not really have to worry about using speakers with an impendance rating of less than 8 ohms. I have a set of Axioms (M80) driven by an ATI1202. I do not have to worry about the receiver going into protection mode.

You can always try it for 30 days. Even after the 30 day period, separate amps are fairly easy to sell, if you still don't like them. My first amp was an Outlaw 7075. When I caught that disorder (upgraditis), it was easy to sell at value(minus shipping charges/taxes). Buy as much amp as you can afford the first time and avoid the common disorder.