Some standard factoids:
Remove any PCI sound cards when using a USB interface. Very rare that they can co exist.
It is also best to disable the MOBO sound card in most installations, It is also rare that they can co exist.
Best practice- use only your trusty audio interface. Why not?
When ASIO mode does not work, there is no reason not to use WDM mode, Cakewalk even recommends this if your read the Audio interface section of the Knowledge base.
It is common for driver installations to not always take properly if something in your system is conflicting, even a video card driver can screw things up.
Sonar is the pickiest DAW on the planet with drivers.
Are you hearing mono in the headphones too?
If not then your wiring is to blame.
You mentioned latency issues. While tracking you want to bypass all efxs and keep things clean.
Use your interfaces direct monitoring, do not use input echo. If your hearing latency in either ASIO OR WDM
mode then your not monitoring correctly or you've loaded down your system beyond it's capacity