The reason H/K sound better, is they usually have very high current amps built in (like Onkyo)
That is a subjective thing, to some people they sound better, to others they don't. Regarding the high current things, Denon, Onkyo, Yamaha all make such claims. Remember the S&V showed the HKAVR330's protective circuit activated after only 0.5 second when tested with a 4 ohm load and delivering more than 25WPC? No wonder they use the word "instantaneous" to describe their high current capability. Again they are honest about their specs!
and even they their amps say 78 watts per channel, when bench tested they usually run higher with only two channels driven and pretty much hit the mark at around 75 wpc when five or more speakers hooked up.
There is no proof for even such claims. HK don't claim ACD either, they specifically say:
"Seven-Channel Surround Modes, Power per Individual Channel :
Front L & R Channels : 75 Watts per channel @ <0.07% THD, 20Hz – 20kHz into 8 ohms
Center Channel : 75 Watts @ <0.07% THD, 20Hz – 20kHz into 8 ohms
Surround Channels (L & R Side, L & R Back) : 75 Watts per channel @ <0.07% THD, 20Hz – 20kHz into 8 ohms"
http://www.harmankardon.com/specifications.aspx?Region=USA&Country=US&Language=ENG&cat=REC&ser=&prod=AVR 354&sType=C
I really hate the term sounds better because more watts does not equate to better sound. You have to remember 90% of the time, your amp is just cruising along at 3-5 watts per channel and it's only during intense battle scenes or heavy explosions that your amp needs breif periods (like a second or two) of real power from the amps (normally around 50-70 watts)
I think you are probably right, but I would say the peak power for those split seconds could be much higher, but part of it would be taken care of by a good subwoofer.
I use all three of my recievers (Denon 4802, Denon 3808 and Onkyo 805) as preamps with outboard amps. Do I need to? Hell no, the amps built in these recievers have great amps, but I do notice slightly better clarity and depth to sound when using amps, is the sound all that much better, not really, I mean it's a hair better, but not jaw dropping or even night and day. Most people probably won't even notice a difference.
You have some of the most powerful receivers. Based on available bench test results the only HK models that could beat any of those receivers in terms of power output are the AVR7200 and 7300. The HKAVR630 did not come close to the tested output of the Denon AVR3805 regardless of 1,2 or 5 channels driven.
It irks me when people claim there speakers opened up with all this power. I shirk because I wonder how? when the amp is just cruising along at 3-5 watts and even during heavy explosions the amp isn't going to come anywhere close to ever crossing 100 watts unless they are listening at insane levels (then they have more to worry about than a 3db increase in the future) or they are listening in very very large rooms.
I fully agree, but I still prefer to have power that I may never need. I have taken enough measurements to know for my own music listening, only classical music that involves bass drums and timpani demands the occasional short burst of high peak currents. Even at those short burst moments, in my room and at SPL that I can tolerate, my receiver alone could handle it nicely but I feel more comfortable to let the power amp take care of the power requirements.
The OP I think the money you spend on an outboard amp will be better used towards room acoustics or a better center (as you mentioned) rather than the minimal increase you might get or might not even notice with an outboard amp.
If he thinks the HK 354 sounds better than his 806, I would bet he is among those who would appreciate the difference (such as what you said about the speakers opening up...) made by external amps.
