It does not say that your file does not exist - this message says that ash cannot find any executable in bin named foghorn1.wav, which should be run. The same way when you write eg. ls - ash then looks for a proper executable in bin and if no results are yielded, returns an error message.
If you want to run a file from current directory, you'd need to write ./my-file, but it only works for executables, which - clearly - a music file is not.
I dont see what the converter has to do with not finding and playing a file
@Marcin-Debowski we haven't experimented with reading the DHT sensors directly using the Omega since they have their own timing sensitive protocol. Because the Omega runs Linux and is a soft real-time operating system, any one of the running processes could interrupt your code and mess up the timing of your pulses.
On Omega2 at least at the RO pin of MAX485 some kind of 5V to 3.3V level shifting is needed.
The simplest solution: put a voltage divider between RO and RX1.
And you should connect the pull-up resistors of input pins (DI, DE, RE) to 3.3V.
RS-485 can be made full-duplex by using four wires ie. two twisted pairs.
Is your Modbus slave full-duplex?
BTW you could build also full duplex config with two of your MAX485 modules. ;)