We have been receiving customer reports of issues with Macs configured with a Fusion Drive and running 10.9 Mavericks. While we have not been able to confirm or test this in-house, it appears that there is in fact an issue with 10.9 Macs configured with a Fusion Drive that can cause audio drop outs and distortion. The issue is apparently widespread, widely known, and affects audio interfaces from virtually all manufacturers, not just PreSonus. The solution will require a software fix from Apple, so in the meantime there are several possible workarounds.
You can read more at these links:
"New iMac Fusion Drive problems - with fusion drive splitting solution "
"Issue #1 - If you own a 2013 iMac with a Fusion Drive (FD) fitted then you wil get audio dropouts and/or clicks and other audio issues. It affects all OS X versions that support FDs"
"Audio problems with new iMac Fusion Drive"
"Potential audio problem with new iMacs"
"Clipping sound on new iMac when Logix X is running"
From this apple discussions thread, it appears the OSX 10.9.2 beta resolves the issue, so a general public fix may be coming soon (though we cannot confirm this at this time):
"Ok, I don't want to spread false hope, but I've been running with the 10.9.2 beta that was posted here a couple of days ago, and I haven't experienced a single drop-out yet."
"Good News: I can confirm that OS X 10.9.2 beta fixes the issue with the Fusion Drive and MBox Mini (and possibly other USB Audio devices)."