Monster Regret!!

I’ve been recommending ZeroSurge for years for high quality surge/rfi protection. Single outlet all the way up to whole house. They’ll even build you a custom device if you want...

Nordost QX4 and QB8 did the trick for me. Clean, clear, open, depth and musical!

Chuck nailed it. Let your ears be the judge. If it sounds the same keep any surge protection for insurance.

Nordost QX4!!

Paul McGowan — founder and Prez of PS Audio — has a gazillion helpful videos on the Ask Paul section of their website.  A few of them answer your question.  Not surprisingly, their view is: use a P-15 or P-20, but if you can’t, go directly to the wall.  Older power conditioners or glorified surge protectors may help things sound "cleaner," but they also usually mute dynamics, imaging, air, depth, and decay because they ruin the low-impedance-output-to-high impedance-input relationship you want as the signal moves along it’s path.   I’ve owned the BHK pre and monoblocks; fantastic gear.  They definitely sound better plugged into a P-15, which I still use for my Audio Research gear, preferring it to the Denali 6000T.  (And, BTW, the BHK pre sounds markedly better with the Tungsram input stage tubes that Upscale Audio promotes for that pre.)  No affiliation between PS Audio and me, but I’m a huge fan of the P-15.