This is an interesting thread as I have a thread in Hardware asking people to see what they get with the loop back test and different audio interfaces. That's a bummer that Cakewalks entry level DAW lacks the offset fine tuning. I'll have to fire up X1LE and see if this is the same. I would think if that feature is not part of the DAW then your hooped. Either use a DAW that includes the adjustment or use an interface that does not have hidden buffers so the adjustment is not even needed.
A few things from this thread I need to point out.
Scarlett 2i2 and 2i4's do not come with Mix Control software. The 6i6, which I have, is the first in the line up that includes mix control. But I assume there is still a ASIO control panel. Set it to 10ms for 90% of the work you'll do. Buffer settings have no bearing on the loop back test results read here:
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http://forum.cakewalk.com/Lets-all-TEST-our-Interface-driver-for-offset-m3178396.aspx The loop back test results will be the same no matter which DAW you use. It may change a little tiny bit from computer to computer, but it is mostly dependent on the ASIO drivers and what they tell your DAW.
Anyway, if your interface is bang on in Sonar x3 it will perform the same in MC , Cubase or Reaper. Changing the buffers can lower or raise your RTL but the offset will remain the same. Hopefully it is bang on or with in a few samples.
Another thing is USB controllers come with their own drivers and this is what matters, your Audio interface is not involved when you use a USB controller. It is involved if you use it's midi ports. Changing audio interface buffers has no bearing on usb midi input latency.
Midi latency is often because your computer is struggling due to DPCL issues or you have plug ins that are adding output latency. By passing all effects is often the solution.