I haven't used Sonar before, so I can't give you the exact steps. In the Save dialouge box, there should be something called "options". It should be in there. You can set the bit rate in there. The common internet bitrate for mp3's is 128 kbps. For your uncompresed wav files: 44.1 k, 16 bit Stereo is considered CD quality, and you will need to have it at that rate in order to burn audio CD's.
My piano sounds like a Steinway if not a Kawai EX in here