Wire instead of stranded conductors! If you still use stranded interconnects or speaker cables, I strongly recommend trying a solid-core cable. It does not have to be one of my finished cables; I also offer kits, and ordinary enamelled copper wire is excellent for experiments.
We live in an age of electromagnetic pollution: mobile data, Wi-Fi, switching power supplies and much more. Their frequencies are usually well above the audible range, but they can generate intermodulation products that mix with the wanted signal or place an additional burden on the equipment. The idea behind termination plugs is to close potential entry points in the form of open, unused connections, such as unused amplifier inputs and digital inputs. Termination plugs are also available for digital outputs. They prevent reflections at an unused digital output from travelling back into the device. Here are a few suggestions for DIY solutions, although ready-made terminators are of course also available:
Some people also cover unused mains sockets. Nothing is short-circuited here; a metal cap is simply fitted and may be connected to protective earth.
An isolation transformer removes the galvanic connection between the household mains supply and the connected equipment. The protective earth on the transformer's secondary side is not connected.
Following a customer's recommendation, I bought an isolation transformer more than 50 years old in a hammer-finish steel enclosure, probably rated at around 1.5 kVA. These transformers are used wherever increased safety is required and presumably also in harbour areas to isolate boats galvanically and prevent corrosion of their hulls.
In my opinion, the transformer should be rated at ten times the power normally drawn from the mains at listening volume. It must not be too small, otherwise the voltage on its secondary side can be modulated in time with the music, producing a tired sound.
The improvement in my system was dramatic. The first word that came to mind was: live! The sound became detached from the loudspeakers and emerged entirely without strain. It seemed as though the speaker diaphragms had only half their moving mass. The frequency range appeared an octave richer at both ends.