Has the other chap had a successful QSO on DMR on his radio? The 'no sound on digital' problem is a known hardware fault that some radios develop (or are shipped with), and if you're both using the same codeplug (which one?) on the simplex DMR channels provided with the settings you mention there's no reason it shouldn't work.
Also, have you tried an analogue QSO? If that works and the DMR contact doesn't - and the squelch is opening, as shown by the green light, then there could be that hardware problem.
But if both radios work on a repeater and the codeplug/channel settings are good, then it's a bit mysterious.