I have never seen proprietary connectors on amplifier speaker outputs, except perhaps for car radios where sometimes they are bundled together with the other wires into a single connector and usually come with a mating connector with pigtails.
There are a few standard connectors sometimes used with speakers, primarily in PA/pro audio settings (1/4" phone plugs/jacks and Speakon connectors) and in very low end home systems that are little more than boom boxes in pieces (RCA plugs, 1/8" or other sized phone plugs). Those are all readily available connectors.
Even if it is proprietary wiring in some unusual cases, you can always splice wires. The wires themselves need not be anything special or proprietary for speakers.