At 8 Ohms and 75 watts, it can only deliver so much current, period. And, it is not high.
What is that receiver rated for at 4 Ohms? If it is not rated, then, it is also not high current into 8 Ohms. Simple. Even if it is, it can only deliver the current the power rating demands.
Now, until HK does its tests with other than resistive loads, one will never know how good their power supply really is. Dr. David Rich, now the tech director at T$Sound, created what is know as the power cubed method, that does test the amps to + and - 60 deg phase shift and down to 1 ohms.

But I bet HK didn't ask him to test their amps.
So, in the end, it is not a high current amp unless there is objective proof or it.
As to your perceptions, it can be very unreliable and biased
So, as others have stated, unless you level match to 0.1dB, and bias controlled, any ones imagination what happened.