Shunyata power conditioner has to be my favorite tweak. The Gemini 8 in my studio probably cost a little more than what I'd call a "tweak" but I purchased an MPC-12 Shunyata power conditioner on usaudiomart that was $650 and put my living room system in a whole different league than before.
I highly recommend for those that can't afford 2k+ on power conditioning, try to find a used Shunyata unit. I'd say it is 80% or 90% of the Geminis improvement in my system for a fraction of the cost. Anyone have experience with the Puron plugs with a Shunyata conditioner? I tried other plug solutions and didnt find they improved things when I had legit power conditioning in the system