you really should not be able to do that anyway...

the ASIO specs require that you use the same hardware for input and output in order to control latency from a single hardware clock.

what you were doing is something called aggregating the audio...

this is a feature possible within the mac operating system and isn't supported by Line6...

and generally the results are less than desirable....

if you are going to ignore this and try to do it anyway, you will need to search aggregate audio on the internet.

here is the apple page with some details:

http://support.apple.com/kb/HT1215

Hey faberglass,

  Are you making sure to follow all of the steps to set up aggregate audio that theRealZap provided?

  It is available at the link below:

  http://support.apple.com/kb/HT1215

  If your guitar is not as sensitive make sure that your guitars volume knob is turned up as well as the Gain on the UX2.

  I hope this helps, let us know if you still have any questions.