OS X controls music devices well–unless you want to run multiple ASIO devices at the same time. Luckily, there is a work around. Here is how I got my USB snowball and my Saffire firewall devices running together.
Apple tends to make music creation simple. However, if you try to get complex with it, OS X can be a little difficult to tweak. For example, if you have an ASIO device connected, it is difficult to use another ASIO device at the same time. Difficult, but not impossible.
Depending on what music software and devices you are running, you will get all kinds of ASIO errors. External of your software, you must tell OS X to let these devices play together.
In your Applications/Utilities folder, select Audio Midi Setup.
Under the Audio menu, select Open Aggregate Device Editor
Aggregate the devices you want to use together. In my case, it is the USB snowball mic and a firewire Saffire A to D device. You most likely will need to set one of them to serve as the clock as well.
After you have saved your device as an aggregate, you should see that aggregate as an input/output option in your software.
For example, using this method I can track from my USB snowball mic concurrently with my multiple inputs from my Saffire device.