Several questions:
1. What service pack are you running for Windows 7 Home premium x64?
2. You mention an update. What update was that? X2a?
3. How many hard drives do you use, what kind of transfer protocol do they use (SATA 2, SATA 3, SSD) and what is/are the RPM's for any of the drives?
4. If you have more than 1 drive, how do you have them set up? Windows will be on the primary drive - which drive holds applications, and which drive holds things like projects and sample libraries?
5. What, if any, analysis and tweaking of any background services have you done, for purposes of minimizing latency and any conflicts? (some antivirus software, for example, interferes with audio processing, and downloading and running DPC Latency Checker will give you an idea of the latency situation on your machine). If your computer was bought off the rack, it will likely have a bunch of bloatware on it that will bog down performance, etc.
6. For your interface, is it plugged into a USB 2.0 or a USB 3.0 port? (some have issue with running in a USB 3.0 port)
7. What settings do you have for your audio interface, for Sample Rate and ASIO Buffer size?
8. In Sonar, what is the Sample Rate set to? It must match the Sample Rate as set for the audio interface.
9. In Sonar, what is the driver mode set to?
10. In Sonar, what is the bit-depth set to, and what is the Total Roundtrip latency showing as?
Let's start with the above, and go from there.
I look forward to reviewing your responses, and to hopefully getting this worked out for you,
Bob Bone