1. Try using the free Google "Chrome" browser instead of Firefox for posting in the Cakewalk forums. Then your posts should format correctly.
2. Are you sure you really need to install a new soundcard for music/gaming? Have you tried using the High Definition Audio onboard soundcard built into your new motherboard? Do you use an A/V receiver or speakers with a digital input, and if so have you tried using them with your onboard sound's digital output?
3. If you do install a new soundcard in your system, then you should disable your motherboard's onboard sound in your system's BIOS setup (the setting is probably under "Peripheral Devices" in the BIOS setup). Then just select your new soundcard as the Windows sound and audio and voice device in Control Panel or the volume control sound devices applet, if it is not already set as the default. You may also want to turn off system sounds, which can cause problems when using your system as a DAW.
4. Audio interface latency can be important when you want to use host-based guitar amp and fx emulation while recording guitar tracks into Sonar, to reduce the delay between what you play on your guitar and what you hear coming back out of your computer. You can find test results of latency and system loading for numerous audio interfaces here:
http://dawbench.com/ 5. In Sonar's audio input and output setup, just select your audio interface's inputs and outputs, not your soundcard's. That way, Sonar will use your audio interface (and not your soundcard).