I looked at the HumX descriptions on the Ebtech site, and it's not clear to me what its design is internally. The product description just talks vaguely about filtering the ground line.
That said, I can't envision any way in which it could be hurting your sound quality, given that it improves your hum situation.
Please note though that their product description sheets caution against using the HumX with power strips, and say in one place that its total current rating is 10 amps (amperes, not amplifiers :) ), and in another place (the document under "downloads") 15 amps. I hope your power amp is not too high powered, and I would look carefully at how much current your system would draw at full power, and leave some margin relative to the lower number (10 amps).
If it turns out that your total current draw is close to 10 amps (or more), try placing the HumX on individual component power cords, one at a time, and maybe you'll be able to achieve comparable results that way.