"From what I know, there is no comparison between the 540 and 640. Completely different components and build. Not to knock the 540 but I'll bet the 640 will crush it."
I'd actually bet the 540 sounds better. The 640 has more power (100 vs 60) and yet weighs about the same as the 540 (as I recall). That means the power supply in the 540 may be bigger relative to power output. In addition, *every thing else being equal*, lower-powered amps will generally sound better. This assumes, of course, that the power output is sufficient for one's speakers. Finally, power costs money, and the 640 is not *that* much more expensive than the 540.
I'd actually bet the 540 sounds better. The 640 has more power (100 vs 60) and yet weighs about the same as the 540 (as I recall). That means the power supply in the 540 may be bigger relative to power output. In addition, *every thing else being equal*, lower-powered amps will generally sound better. This assumes, of course, that the power output is sufficient for one's speakers. Finally, power costs money, and the 640 is not *that* much more expensive than the 540.