Same old debate
This reminds me of an old article I recall from The Audio Critic in which they did a double-blinded study comparing a $300 Pioneer Receiver vs. some expensive amps (Boulder).
TAC Result - they could not even hear the difference, which blows everyone away.
TAC Conclusion - all amps sound alike in double-blinded studies, but the sound processors differ in sound quality.
I think there are too many variables to consider - speakers, room acoustics, processors, and original source.
With all that being said, just being an Audioholic makes you want to buy an external amp whether you need one or not.
Heck, I'm thinking of getting a 1000 watts/4 ohms x 5 Ch amp ($3K) myself even though I don't think I will ever hear a difference.