Does the heat an amp puts out have any effect on the sound quality ?

Don, the relevant specs on your equipment are:

Speaker impedance:  6 ohms nominal, described as "easy to drive."

Amplifier:

Rated Continuous Average Output Power (both channels operating simultaneously, 20 - 20,000 Hz):
150 W/ch 1-ohm load (1-ohm operation possible with music signals only)
120 W/ch 2-ohm load
60 W/ch 4-ohm load
30 W/ch 8-ohm load

Power Consumption:
160 watts idle
260 watts in accordance with IEC 60065
200 watts for rated output into 8 ohms

Maximum Dimensions:

Width 465 mm (18.31”)
Height 191 mm (7.52”)
Depth 428 mm (16.85”)

Weight:

24.7 kg (54.5 lbs) net

Consistent with what you have found, I would not expect an amp having size and weight as substantial as the E-600 and dissipating (consuming) roughly 200 watts to get particularly hot.  The same dissipation in a much smaller package would be a different story, though.

Regards,
-- Al
  

well, for the sake of discussion then......

I've a vintage Yamaha CA-2010 integrated which has a switch on the front to toggle between Class-A & "Normal" (which is Yamaha speak for class-AB). in class-A it is also a 30W/ch into 8 ohms just like donjr's Accuphase E-600. in my particular case, the amp's heatsinks (in the middle of the amp) become really hot. In the manual i read that the quiescent bias for the output stage is stepped up to 300mA in class-A while it is just 25mA in class-AB. The amp has no forced cooling & it is vented on the top + bottom + back. I suppose that Yamaha intended to operate with this sort of heat dissipation....
Could it be possible that the Yamaha's heatsinks are much smaller than the E-600's hence the higher heat??
The dimensions of the amp are quite similar to the E-600 & it's just 8-9 lbs lighter.  

Bombaywalla, here are internal photos of the Yamaha CA-2010 and the Accuphase E-600:

CA-2010 internal view

E-600 internal view: On page 3 here.

There may be somewhat more heatsinking on the E-600, which perhaps contributes to the weight differential, but it’s hard to tell for sure (in part because the height of its heatsinks isn’t apparent in the photo).

Perhaps more significantly, though, I see that the CA-2010 is specified here as being capable of providing:

2x 120W (Class B, 8 Ohm, 20Hz...20Khz, 0,03% THD)
2x 130W (Class B, 8 Ohm, 1Khz, 0,03% THD)
2x 140W (Class B, 4 Ohm, 20Hz...20Khz, 0,03% THD)
2x 180W (Class B, 4 Ohm, 1Khz, 0,03% THD)
2x 30W (Class A, 8 Ohm, 20Hz...20Khz, 0,03% THD)

And has having power consumption as follows:

600W / 700VA (USA / Canada)
900W (EU)

I see three relevant implications in those numbers:

1)Although the test conditions upon which the CA-2010 power consumption numbers are based are not explicitly specified, all of those numbers are far greater than the numbers for the E-600.

2)The relatively small increase in the power capability of the CA-2010 into 4 ohms vs. 8 ohms would seem to indicate that it is not designed in an especially robust manner, which would seem consistent with a greater rise in internal temperatures compared to a more conservative design.

3)The fact that the CA-2010 is specified to operate in class B at much higher power levels than in class A would seem to suggest that its internal B+ and B- voltages are likely to be much higher than in the E-600. Which in turn would seem consistent with its much higher specified power consumption.

Best regards,
-- Al

there is no doubt in my mind that the E-600 is a better designed integrated & it is also accordingly priced. These 2 amps come from a different eras of audio - 2009 for the E-600 & 1977 for the Yamaha.
yes i did see that the specs of the CA-2010 indicated a not very robust power supply for hard-to-drive speakers. Luckily for me the speakers it is driving are almost flat 8 Ohms; so, very little stress on the amp.
thanks for taking the time to research these 2 amps & compare their specs......   

Heat good...cold bad !