What audio interface device do you have? You must have a compatible audio interface device to use with MP9.
I recently (within the last month) installed MP9, but I have a compatible device an MAudio Fastrack Ultra 8R USB connected recording interface and MP9 automatically detected the device and set it up as the sound device.
The keystudio 49i is NOT an audio interface unit.
Here is the Avid list of hardware and the many MAudio interface devices that are compatible with MP9:
http://avid.custkb.com/avid/app/self...p?DocId=408271