It sounds like your speaker system predates HDMI's adoption, or was never intended for use in a home theater system. Even the lowest budget soundbars will inclu

It sounds like your speaker system predates HDMI's adoption, or was never intended for use in a home theater system. Even the lowest budget soundbars will include an HDMI port and support ARC. I am surprised your TV has coax SPIDF but not toslink, as it was the gold standard for home theater audio before HDMI came around. It sounds like you just got bad luck with your TV having a bad 3.5mm jack and not supporting toslink, as most I've seen will at the very least support the latter, and often have a separate "line out" port for the former.