Tube guy - "Cables don't make a difference"
and that from someone who uses vintage cable??? You have just got to be kidding.
When trying to make a good sounding mains cable I can show you around 20 ways of not making it.......................... I know there are lots of high priced poor value for money cables out there and your admission of $20 interconnects tells me they are home brewed and probably tuned to your system. Tannoys and 300B's says a lot about the path you have already been down.
The cable required varies according to what piece of kit you are running, i.e. double insulted CD players do not benefit from an earth wire as they only have the hot and neutral connected at the device. Power amps have different requirements to pre amps etc. Usually most systems are earthed via the power amp which can prevent earth loops. I still prefer to have all the cases for music gear at the same potential so will not lift earths. Anyone who's ever got the earth belt will think twice about messing around blindly. Some equipment also have built in mains filters which dump noise to earth and in the absence of a proper earth will give you a nice belt if you touch the case and something earthed that will wake you up sharpish, beware.
Shielding of the cable with the earth is a good idea but difficult to achieve practically.
I have found wildly differing results from the quantity of copper contained and the number and geometry of strands, even insulators make a difference. It was shortly after I demonstrated mains filters and mains cables back in the 80’s that they became ‘flavour of the month’ and every one jumped onto the bandwagon to high prices.
A recipe that works pretty well and remains relatively flexible is high voltage test cable plaited together, it comes from RS and Farnell in several colours and is not expensive. The way I look at mains feeds in audio is a cricket bat smacking your butt every 50th of a second, it’s a mechanical shock hitting the primary windings in your transformer and then after it has set the cores vibrating it goes onto strike at your diodes, the capacitors have to damp this shock wave into something resembling pure DC, a big ask and probably why PIO caps do a better job as they damp better than electrolytics or polyester etc at lower frequencies. Going back to the cable the harder the insulator surrounding the conductor also affects the sonics.
All this harps back to the usual arguments that 1 metre of cable after hundreds of kilometres of mains feed cannot make a difference, well to all those naysayers water filters work and so do having mains filters and specialist mains cables. IMO they can either destroy or make a system and do not mind demonstrating this to nay sayers. Looks like a piece of wire is not just a piece of wire. The best cable I ever made was a platinum feed with a 36 amp capability, trouble is it was bloody expensive and was bought by a dedicated audiophile back in the UK who uses it with Cary valves and Klipshorns, he has very good ears.
Start at your consumer inlet and wire in a dedicated ring main just for the audio, >30 amp should do it or if that proves to difficult / expensive then get yourself some ‘ for audio mains cables’ and start enjoying the benefits.