I have a FT991a that the sound card took a crap on me and Yaesu said it would cost $700 or more to replace it. I am thinking to find an interface that won’t cost a fortune. I thought about a SCU-17 but they cost $200 and I am on a tight budget {Social Security doesn’t go all that far). So can I get the Digirig and cables and make it work and not be to complicated to setup?
setup would be pretty straight forward. you would just change the settings in your software. point to the ‘new’ soundcard and ‘new’ serial port instead of the ‘old’ built in soundcard/serial port names/numbers.
that looks to be a match for the ‘alternative’ connections on the ft-991a rear panel.
you’ll need a digirig mobile in rs-232 configuration to go with.
I’m just guessing though, i don’t own your radio so i’m just looking at pictures 
@K0TX might have a more definitive answer
good luck
kb0wlf