What a bunch of hoohey!
There was actually an AES article or three that were written about fuses and audio. No audible effects were ever found.
The reason I mention I am underdriving them is my current Onkyo is 15 years old and is 55W rated.
Only a problem if you need more than 55 watts to play your speakers the way you like them.
The Quads sound great, and get loud but I notice the mid bass starts to soften at higher volumes and I can get some distortion, which makes be believe they are not being controlled sufficiently.
The most likely source of this situation is that the Quads themselves are compressing the signal.
Here's the theoretical maximum undistorted SPL you can get out of a 6 1/2 inch driver: Every real world 6 1/2" driver can be reasonbably expected to do worse:
F,Hz Max SPL, dB
At 80 Hz you are limited by the theoretical maximum capabilities of your speakers to a mere 105 dB which corresponds to a mere 50 watts given the rated sensitivity of the speakers.
You already have enough receiver to overpower the speakers.
Remember that the estimate above gives the speakers every possible break, while our receiver numbers are likely to be far more accurate.
IOW you are probably already overpowering your speakers with 55 wpc.
Remember that to get twice as loud you need 10 times the power. In your case this would be 550 wpc, and you don't have the speakers to handle such an amp!
Going to 85 wpc or 125 wpc is like a drop in the bucket, and just so you don't forget, you don't have the speakers to handle such an amp! You really don't have the speakers to handle the amp you got.
You would be in far deeper hot water if you didn't have the sub. You might want to experiment with a higher subwoofer crossover frequency.