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Are you using the Yamaha's Pre-out or Zone 2 out to feed the 2x4hd? Note the pre-out should be going direct to a power amp not another pre-amp which the 2x4HD effectively is. It sounds like you need to be totally bypassing the Yamaha's volume control so use 'zone 2' out or (if such a thing still exists) 'tape' out!

@penguinpages I'd temporarily try using the zone 2 out and see if the problem goes away. Make sure to turn the master volume down on the 2x4HD before you do. In the plugin set the inputs to 0db and check the output tab in the plugin and make sure all the channels are set to 0db so you've a known starting point. With signal plying see if increasing the master vol of the 2x4HD gets you to a high volume without distortion. If it does you'll know the issue has something to do with the settings of the pre-amp out. 

Are you feeding the 2x4hd from the Zone 2 or Pre-out of the Yamaha? A power amp should be connected directly to the pre-out instead of another pre-amp, which the 2x4HD basically is. snow rider 3d

thanks ,you helped me

Thank you for your assistance. idle breakout