To be clear I have an existing Decware cable that sounds great, but is
unshielded. I’m not trying to DIY a new cable from scratch. I just want
to add shielding to see if that solves my noise problem.
Right, so .... if you like your cables, don't hack them yet.
Use inexpensive shielded first. That is, use the Belden as a prototype. If you like your results, then you know what direction you want to go in. The goal here is not sublime purity of essence, but to prove/disprove your ideas of noise elimination. Do it cheaply with cables you don't mind throwing away before you hack things you love.
Best,
E