Today, Apple announced the availability of their latest Mac OS X release, 10.9 "Mavericks." TASCAM Engineering has determined that our USB drivers have issues in the new release.
This issue affects all current "US-" series interfaces. We are already hard at work on updated drivers, and plan to have those ready as soon as possible. Our recommendation for all new OS upgrades is to wait for reports on how your software will function in the new system. In this case, we recommend waiting until the new drivers are available for your TASCAM interface before making the upgrade.
In addition, the latest version of Safari (6.1) may have problems playing back audio through TASCAM interfaces.