Ok, so I opened the M-Audio:
![](http://lh4.ggpht.com/jomanos/SOAMf8dYmXI/AAAAAAAAAsw/H1Y8ZtrbpXM/s800/m-audio_pcb.jpg)
![](http://lh4.ggpht.com/jomanos/SOAMfmXNTVI/AAAAAAAAAss/W4D8FR0ogXo/s800/m-audio_output.jpg)
The seems to be enough space to do some work. Here are my thumbnails for what I plan to do:
![](http://lh4.ggpht.com/jomanos/SOAMgQtKOfI/AAAAAAAAAs0/-pTMiyBHnKY/s800/m-audio_schematic.png)
The simplest option would be to solder some resistors to ground as in Option A. Or use a 1:1 line output transformer as in Option B.