[Herald1360]

Unless you're dead set on originality, solid or stranded inner won't make any difference at audio frequencies.

For solid inner, you would be better looking at miniature RF coax than audio or microphone screened cables- by their very nature these need to be flexible and so will be stranded. At UHF frequencies in miniature coax, solid inner provides more closely controlled dimensions to provide better constancy of the characteristic impedance.