I have no expertise, but this sounds similar to a problem that I am having with a Xonar DX. I get no output from the speakers since Mint 14 (& 15, & 16). 13 is the last version that worked for me.
You mentioned that your DGX input works in Windows. Do us both a favour and check if a live-USB instance of Mint 13 fixes your problems.
There is a chance that your issue is similar to mine: viewtopic.php?f=49&t=118289&p=797528#p797528