what part of your amp only does 50-100 ACTUAL watts do you not understand? When you force your amp to do 400 watts, you are clipping. What part of BOSS always lies on their amps do you not understand? What you see on your multi-meter is not real RMS power, your multi-meter is NOT an amp RMS wattage tester. It does not put a resistive load on the amp right at ohm loads and actual show proper rms wattage like an actual Amplifier dyno. The picture I showed you is not some cheap multi-meter, its actual amplifier testing equipment. With the AC voltage on the multi-meter Any amp can be overdriven to a high voltage however if you put an oscilloscope to actually show the signal, it wont be clean at that voltage.
You have people with 5000 dollar amp testing equipment showing boss amps only doing 1/10 of the power thats on the sticker and thats a consistent number throughout ALL boss amps being tested, yours is no different. You need to stop being dilusional about your amp making 400 RMS because its only making 50-100 at best.