My Harmon Kardon Onyx Studio 2 had booming bass and distortion issues. There was a two button combination that would change built-in equalizer setting: Hold Bluetooth button and - for ten seconds for bass. Hold Bluetooth button and + button for tremble. The settings wouldn't hold. I ended up buying a Studio 2 motherboard from a vendor on eBay located in Lithuania for $30, and the replacement solved the problem. The repair required special torx screwdrivers, but was otherwise and DIY easy fix.