Can I send audio through coax cables?
COAX to RCA adapter

You could get a "Y" adapter but it doesn't matter because you are getting mono.  The Y would just split the mono in two.  

For stereo it is doable but the only thing I know is S/PDIF - so search for a COAX to S/PDIF adapter.  

Either way I wouldn't spend a lot of money on adapters.  You are getting mediocre end product no matter what you spend.  Go to the local radio shack and enjoy your music today.