I lost my reply yesterday also. Are you 100% it ain’t the amp? Crossing over above 75hz might be a xover in the sub. I had distortion coming from a pair of speakers that I didn’t notice at low volume because with the clean bass output the amp distortion went unnoticed until turned up. Fortunately for me I have multiples of amps, speakers etc I was able to diagnose the problem myself. Maybe in your situation you can ask revel service for some values and pick up a cheap multimeter?
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