In Olex, you should be able to go to the layers menu and "show data flow" and it will show the data coming from the sounder and the list of sentence types (data types). To do hardness in Olex, you have to pay extra for the HT module.
I like the Actisense opto-4 cable to hook Furuno sounders to PC serial port. That will work with no drivers to install.
There are some USB-rs422 adaptors but some have linux drivers and some don't, and older Olex operating systems have limit of 4 serial ports; too many variables for most people unskilled in the operating system details.