I would do the same as thomasschw7 or, if better speakers are available, connect them to this one and dispose of the corresponding speakers.

I took any cable, speaker cables are not demanding (but there are specific speaker cables by the metre in DIY stores or digitec etc., they should simply have at least the same cross-section). For the extension, I cut the cables and reconnected them with lustre terminals. Soldering also works. A tip for soldering: Cut the individual strands about 2cm apart. Then the insulation (e.g. with adhesive tape) is easier and there is no very thick connection point.