Sonar comes with some really nice soft synths, which you will like much better than the cheesy MS sounds.
The TTS-1 is a nice GM synth, and is multi-timbral, meaning that it can play multiple sounds at the same time. (you can have a different sound on each of 16 midi channels, or could assign multiple sounds to the same midi channel, or combine those approaches as desired).
It will require some investment of time into learning the ropes with Sonar, but if you go through the tutorials and videos, and consider picking up one of the REALLY well-written books on Sonar, you will get up to speed MUCH faster, and create much higher quality work in the process.
Just a heads up - IF you are not currently using a dedicated audio interface with Sonar, you may begin having dropouts and crackly noisy sound, once you start using the soft synths, or get into larger projects. If this happens, it is because of all of the massive analog/digital conversion that has to take place all being handled by your CPU.
An audio interface has dedicated circuitry to take over that daunting conversion of conversion, and is really a needed component for using Sonar. A basic interface will run from around $120 to around $160, and fancier ones with more inputs can run up to and over $500.
I know the above was not part of your questions - but I thought you might want to know ahead of time, so that you can prepare for adding one to your budget at some point.
Bob Bone