I bought these as kits from Aliexpress - they provide a delayed start (muting) and DC protection for speaker outputs. I ran them from the +15V outputs on the PSU - they're designed for AC input but I just removed and bypassed the rectifier and connected directly to the 12V regulator instead.

Note that they have a common speaker ground, so when reversing speaker connections on phase-inverted channels do it AFTER the protection circuits, not before, to avoid unintended speaker shorts. I learned this the hard way, which cost me a power supply and a L15D board (fortunately I was able to repair the latter with a new IRS2092 chip, mosfets and 5.6V zeners).