the twisted wire will filter out minor interference - the BMW engineers can use the twisted wires as they carefully calculate the path of every wire, factory and authorised retrofits... when you introduce your own wiring, you face a chance of picking up alternator whine - that whine can't be compensated by the low number of twists in the speaker wires, you need to further isolate the wires from picking up external noise... to do so, you need shielded wiring, with grounded shield - the power to amps needs to be cleaned up, as some amps can't clean it up internally to satisfactory level... as a matter of fact, you can't go wrong with shielded wires, as in coax wires in video applications...

use 1-pair (2-conductor) shielded cable for the power supply...