That's because S/PDIF isn't a type of connector. It's commonly carried over coax cables (with RCA connectors) or optical cables (with toslink connectors).
I have found toslink and SPDIF to be both very reliable in this though (probably since they are such mature technologies at this point).
Make sure your TV is actually outputting the correct format over Toslink to your soundbar - many times they default to 2.1 instead of 5.1 or the wrong format (Assuming you have a soundbar with more than just 2.1). A lot of TV's also downmix to 2.1 audio if you pass through a source to them and then use the Toslink output of the TV to a receiver (like say if you did Apple TV --> TV --> Receiver)
What brand? It's impressive when they last that long.
Older receivers (1980s) can blow an output transistor, which is a pain (fixable if you are skilled). Newer receivers are often built with integrated power amps that have extensive protection circuitry... they're truly impressive, and hard to accidentally damage.
I've done some amplifier repair work. The amplifiers I repaired were typically much older (1950s, 1960s). The most common failure modes are fuses blowing, potentiometers failing, capacitors failing, and PCB-mounted jacks failing.
I suspect that it didn't have enough airflow, though.
Anyway, I was ready for ARC2, so I just replaced it with a Sony. I'm extremely happy with the new one.