As a general rule, our mixes will not be as loud as commercial releases.
However, there are some things you can do.
You definitely want to watch those peak levels to avoid digital clipping. But perceived volume comes from RMS levels.
Judicious use of compression can help.
I'm not sure what 8.5LE came with, but you can right click the FX bin of your audio track to see if you have the Cakewalk compressor.
If not, this is a good place to start:
http://www.store.cakewalk.com/b2cus/ProductInfo.aspx?productid=35-CWF11.02-10E This is a free download of some basic effects that were included with many Sonar packages.
Sonar 8.5LE supports third party VST plugins, ranging from free to quite expensive.
If nothing else, get VoxengoSPAN. Plug it into the FX bin of your master bus. It doesn't affect your volume, but it is a great tool for keeping an eye on your final output.
You can try normalization. Some like it. I don't. Be aware that normalizing will permanently alter your original file, and you can't go back.
Experiment with some limiters and compressors.
You have the right idea on your incoming signal. Keep that clean. If you start with a good signal, you have a lot more room for manipulation.
When it's all said and done, you may still want to tweak the volume knob, just not as much.