Rumor has it that less expensive receivers and amplifiers use a different curve than more expensive stuff when it comes to volume controls.
It is said that on the lesser models, a small turn of the loud dial produces a lot of volume early in the knobs travel to give the impression of greater overall volume.
"Wow!! I've only got it turned up a little bit, and see how loud it is!!
You may be getting all of the quality amplification that the amp has to offer in the first 50% of travel, and distortion and clipping in the rest!!
Caution may be required while operating in the upper realms!
......that is, until you get your new amp!!!