Twisting positive and negative lowers inductance (important) and increases capacitance (not important). It also makes cable immune to electromagnetic and capacitive noise pickup (and radiation). Twisting two already twisted cables is different and doesn’t serve any purpose. In fact, cable manufacturers go to exotic schemes, like helical twist on hollow tube or flat cables (made of multiple twisted pairs) to split thicker wire into multiple isolated strands and then separating them, so that each strand is exposed only to magnetic field of neighboring strands. All thing comes from skin effect phenomena that becomes relevant in copper at 18awg @ 20kHz. That at least is the reason for such designs, but I doubt it is audible. I would just keep them apart. Adding second cable will reduce overall inductance, but I suspect that your intention might be different. You probably think of better damping of the membrane by reducing resistance in series. That won’t make any difference, since for the purpose of damping there are already many ohms of speaker’s own impedance in series (source impedance) and two wires in parallel would improve it only by a fraction of 1 percent. Lets us know how it sound with and without added cable.