FYI - This is from the Presonus FAQ -
AudioBox 22VSL - Can I use the AudioBox 22VSL's inputs to record a Line Level signal?
Technical Support August 12, 2011
The AudioBox 22VSL inputs are designed for passive input signals (microphones, instruments, etc). This means that they have a much higher gain than is necessary for recording a line level source. The AudioBox 22VSL's microphone inputs can be used to record a line level signal if your line level device has a volume control and you have a Direct Box. To begin, first connect your line level device to the input of your Direct Box. Then connect the output of your Direct Box to an XLR input on your AudioBox 22VSL (do not use the 1/4" connection for this). Make sure both the output level of your line level device and the input trim on the AudioBox 22VSL are set to their lowest settings.
Please note: if you have a Direct Box that also includes a -20dB pad, you can connect a line level device that does not have its own output control.
To test how hot your Line Level device is, turn its output level to the unity setting (consult the device's documentation to determine this setting) and slowly increase the trim control on the AudioBox 22VSL. If you cannot keep the input from clipping, lower the output level from your line level device or engage the -20dB pad on your Direct Box (if it has one)