Paying a professional to create a digital room correction filter for me. I figured out later that I needed to swap the position of my couch and my speakers (never have your listening chair in the center of the room if your speakers are against a wall). It seems my system is too revealing - any digital attenuation comes at the cost of a palpable image, lower dynamics, less rhythm & pace.
Your single most significant purchase mistake?
Your most significant regret for having bought? Big expectations and an even bigger letdown? The one you kicked yourself the hardest for ever having bight