I have been informed that the 2i2 does not come with the same ScarlettMix software I have with the 18i6 however there must be a way to change the buffer settings on it. I would recommend giving the 2i2's manual a read to find where you can change the ASIO buffer setting.
Otherwise in Sonar go to Edit > Preferences > Audio-Driver and click ASIO Control Panel (or whatever that button says... I forget) and it SHOULD open whatever is controlling the 2i2. From there you just look for where you can increase or decrease your buffers (in MixControl you just click Settings and it gives you a list of buffers in milliseconds... the lower the number the lower the latency... the higher the number the less strain is put on your system which avoids dropouts and other problems)
You should also make sure you only have the 2i2 selected as your ASIO input device in Sonar Preferences but that is all described in the Tutorials section of the Sonar manual (which you may want to take a look at as well because it could help you solve a lot of issues regarding setting up interfaces and whatnot).
Anyway... you will probably do much better with the 2i2. It'll just take a bit of fiddling to get it set up.
Read the 2i2 manual and read the Sonar Tutorial in the manual and all should become clear.
Cheers.