Speakon and 1/4" phone plugs are industry standard for heavy duty audio connections, typically on high power amplifiers. They hold up well and you can use heavy guage wire. As for solid copper wire, it's way too stiff to work with and most connectors will suffer a demise from it. Low oxygen speaker wire is supposed to be good stuff but is pricey. I simply use stranded #14 two conductor w/ braided shield. I pump a conservative 300watts rms per channel through it without any ill perceived sonics. Sometimes people get too hung up on the use and specs of connecting cables, gold connectors and such, often not realizing that the tiny bit of sonic difference can only be detected or measured with specialized equipment.... not the human ear. Gold connectors are a marketing scam, especially when the entire audio signal path isn't seeing gold connections !