You may be confusing inputs and outputs.
Make sure that the single coax RCA connection says digital audio output. You may not be able to find a soundbar with coax digital input but you could use a coax to optical digital audio converter to connect any soundbar with optical input.
If you have an HDMI connection which is labeled ARC then you can use a soundbar with an HDMI connection that can work with ARC.
Make sure that the 2 RCA jacks say audio output not input. A soundbar with aux input would work.
What does you TV Have? TOSLINK, Digital Coax, HDMI, RCA? Also you need to consider what Soundbar you buy and what it has as inputs.
Rca, HDMI, coax
1. Digital Coax on a TV is always output
2. RCA's have ptions for input/output and should be printed on the back of the TV, if not refer to the manual.
3. HDMI you also need to refer to the manual because most of the time "ARC" or even Input/ouput isn't labeled. Lower end TV's would have 2-4 HDMI's but they are separate channels designed for Input only.
What is the Model # and it can be explained further.