I have a pioneer avh-200ex headunit.
Amp is a orion 2500d.
I know head unit maxes without distortion. I then hooked up my dd1 got signal and 40hz light on. I slowly cranked it up I would get a distortion flicker. I back it off the 40hz light goes out until I turn it back on to not get distortion light. I have my gain set to around 96% any higher in have distortion light fully on. Using track 5 and have used power ground with the + terminal.
My amp not a quick replace as it's a discontinued amp and dont want to fry it.
Also have one of the self build oscope with x100 probe and shows same but just never had an aml able to push gain almost max.