[mcuneo]

A few things that might be useful to check on the firestudio:

Make sure in the outputs/router screen (- playback tab) that DAW 1 & 2 line up with the assign for the L and R of Phones 1.
If you are using a mix source instead of directly routing the DAW's to outputs, then you need to make sure that in the Mixer DAW 1 is panned hard L and DAW 2 is panned hard R.
Also make sure all the settings in Hardware Settings fit what you're using. ie, sample rate matches up with what the setting is in Logic (SHOULD change automatically but sometimes doesn't if you're using other hardware as well or switching between programs with different sample rates) clock source is internal if just using the firestudio.
Also try the different operation modes. Normal mode should work (I don't have any problems with it). Upgrading the software from the presonus website also might help.

Hope some of this might help with your problem.