I plugged my Roland MT-32 into the line-in jack on my ensoniq sound card, and got no sound out of the speakers. None at all.
The system is running LinuxMint, and when I checked the audio-in devices, it shows input activity when the MT-32 is outputting midi.
I connect the MT-32 to a bluetooth speaker I had (via the speaker's aux port) and I get sound.

If my line-in were dead, I would think I wouldn't get any activity when using the MT-32.
Is there some software setting I have to do to direct line-in to line-out?