I agree with others - there is no need to use shielded speaker cables.
Firstly, they carry huge signals compared with interconnects of phono cables, so any RFI will be miniscule in effect.
Secondly, because a speaker cable is a pair of wire bundles, what affects one bundle pretty much affects the other in the opposite way - this cancellation effect is crucial for very high speed cables like ethernet, which mainly uses unshielded twisted pairs these days.
Thirdly, adding a shield will increase the capacitance of the cable, almost always for the worst.
Speaker cables may benefit from being gently twisted but most often the two conductors will also be separated by about an inch.
Similar arguments apply to balanced interconnects. Balance is good because it increases the signal to noise ratio. Shielding is debatable.
If cables must cross other cables, try to do this at right angles to minimise interference.
I'd caution you about centre speakers, but it is off-subject! Nevertheless, have a good look at this Discover the Surprising Flaw in Center Channel Speakers