Well the same points still apply:
- most speakers in a small domestic setting which is less than 5x8 sq. metres will work fine, especially if there is a subwoofer or two to take care of the more demanding bass frequencies
- if you do have more demanding speakers - < 86db, 4 ohm designs, full range speakers etc
- if you have a much larger space
Then a power amp might help.
Now a power amp is first and foremost, muscle, so it helps to improve the dynamics of your system.
So make sure it has at least 1.5 times the rated specs of your AVR, otherwise it's not going to be much help in improving dynamics
If you want sound quality as well as dynamics, then be prepared to spend more.
There are many power amps which give better dynamics, but less will provide better sound. The processor section of your AVR will also determine the amount of improvement.
IMHO, if it's better sound you are after, a better set of speakers will make a bigger difference.
As for the use of a stereo amp with HT bypass for this purpose, I think it's a good idea. You switch off the AVR, and switch to stereo playback with only the stereo amp driving the front pair of speakers.
So take into consider why you really want a power amp:
- ego? I want to power my speakers with a massive amp, even if it's not needed
- personal belief - just like some will insist that antibiotics are needed for viral flu
- or the reasons given above to improve sound
Once that is out of the way, then decide based on budget, sonic preference and whether you need it for critical listening, or mainly for HT.