See thread here for background:
I am bringing the thread to this subforum so as not to continue the off-topic discussion in that thread.
IME in most domestic situations a modern flagship AVR has enough juice to drive most speakers even if they are rated at 4 ohms nominal impedance IF you drive only two channels.
Nevertheless, if the room is large, lets say more than 60m3 and you like to listen to music at high volume levels, an AVR may not be enough. IMO the main reason is the PSUs of modern AVRs are not what they use to be 10-15 years ago. Modern AVRs have all the bell and whistles but they tend to be anemic. You can verify that if you open any AVR and check the fuses current rating.
This fact sometimes justify the use of a separate power amplifier.
I didn't mention any problem with AVRs. I only referred to the fact PSUs are anemic in last model AVRs, perhaps with due exception of flaghip AVRs.
For instance my current Yamaha RX-A2010, rated @ 2 x 140Watts/channel, 20-20000Hz, measured like this:
It is easy to figure this out if you open the amp and find the PSUs' fuse rating at 3.5 Ampere.
Suppose the fuse was selected with safety factor equal to 1.2. Then you have safe 2.8 ampere to work at 127Volts, which means 355.6 watts to share between all channels and pre/pro inside the AVR.
My calculations are 172.8Watts @ two channels driven simultaneously, 69Watts @ 5 channels and 50 Watts @ 7 channels.
And this is the second AVRs in Yamaha's Aventage series.
Then I opened an entry level AVR and find a 1.5 fuse in the AVR rated at 90 Watts/channel and I started guessing what the manufacturer is trying to sell...
Yes, I know 8-10 Watts are enough to obtain more than 90dB in a small room in stereo mode, but what happens with dynamic peaks as high as 10-15dB in a large room using speakers with 86dB sensitivity at 4 ohms nominal impedance? You need POWER to follow music dynamics... Only a flagship AVR has the guts... or you need to buy a separate amp.