Of course there is a difference. You are in a position to compare mass market equipment (Sony, Pioneer, Yamaha, Onkyo) with upscale equipment (Bryston, Creek, etc). If you hear a difference - and I know you will based on comparisons I have also done - then it exists....regardless of what others what you to believe.
You are seemingly comparing an integrated (Creek) with an amp (Bryston). Was this intentional? As mentioned, your Bryston is an excellent amp - but not simply because of power output. The Creek is also an excellent amp, but not directly comparable, unless you plan to bypass the preamp.
A note to all the people who mentioned "Increased Electric requirements" - simply because an amplifier mentions output (sonic) of 500watts, this does not mean that the draw from the local utility will be enough to be billed for 500 watts.
BTW, the difference in the amplifier output classes - to be simple - is to eliminate transistor anomalies when the waveform switches from positive to negative sections of the waveform. There are other reasons, but the main one is to stop the switching issues.
