Shielding speaker cable adds capacitance, which acts as a 6dB/Oct low-pass filter. The longer the cable, the greater the capacitance, and the lower the frequency at which the low-pass cutoff frequency occurs.
Speaker level signals are much higher level than line level. like 20 or more dB, and so much less subject to audible effects. Twisting the wire results in equal noise pickup in both wires, which is cancelled at line level by the common mode rejection of the terminating end input. Balanced line feeds excel at cancelling this because noise is induced equally in both halves - Common Mode - and is measured by calculating the Rejection Ratio. Put together you have the CMRR. No such capability exists in a speaker, so twisting does nothing meaningful at speaker level.
The bottom line is using high quality bulk unshielded 12 ga. speaker wire for home theater runs of 25 ft is perfectly adequate. Here is one source: https://www.gearit.com/products/gearit-12-gauge-speaker-wire-cl2-rated-in-wall-ofc-oxygen-free-copper-cable-99-7-home-theatre-car-speakers-more-12-awg-pro-series-cl2?variant=30330652622957