I’m using Cubase Artist 6 on a retina display macbook pro running OSX 10.9.1. I recently set up a PreSonus AudioBox 44VSL digital audio interface. The interface works well with other programs and audio sources, so I think the problem lies with Cubase. The output sounds over-driven and somewhat tremulous. Reducing the buffer size in Cubase makes the reduces the tremulousness of the output.
CA6 is discontinued and is not officially supported for 10.9. That said, there is a workaround that often helps.
Have you done this update for 10.9 audio? https://www.steinberg.net/en/support/knowledgebase_new/show_details/kb_show/workaround-using-older-steinberg-software-under-mac-os-109-mavericks/kb_back/2025.html?tx_p77sbknowledgebase_pi1[keyword_search]=CoreAudio2ASIO