Latency

Most interfaces will have latency and 10ms is average. 

To deal with it you monitor at your interface listening to a blend of your input ( guitar ) mixed with the output ( computer ) Sonar automatically adjusts the playback timing so your input will be in sync with the other tracks. 
Do not turn on input echo or you will hear the latency as a delay sound. 
Also while tracking disable any EFX by bypassing the efx bins. 

ASIO isn't a magic bullet; you can get 5.8ms with WDM too. Some vendors' drivers do work better with ASIO, though. You have to try both.

Because latency is unavoidable, SONAR does its best to compensate for it. It figures out the latency from buffering, data conversion and plugin processing and makes everything line up properly.

If you record a new track and notice that it's not lined up with your previously-recorded tracks, it's possible that there is unaccounted-for latency. I won't go into how that can be; let's just say SONAR doesn't always know about every source of latency. 

For those situations, SONAR provides a manual offset. On the audio options screen you'll find a box labeled "offset", or "manual offset", I forget which. Figure out how many samples off your tracks are and enter that number in the box, usually as a negative number assuming your tracks are late. SONAR will then add that to its own calculated latency number and everything should line up perfectly from then on.

Sonar is one of the most picky audio application when it comes to the interface and especially the drivers. 
It works best with ASIO or WDM drivers supplied by the manufacture of the audio interface. Both are of equal quality. 
 Sonar does not get along well with on board sound cards which will require MME drivers or using asio4all (which is a WDM driver actually.) 

Best performance is with the ASIO or WDM drivers and using only one device. That way the clock source stays the same and stable. 
Nothing wrong with using a headphone output if that's all there is. 
You might find yourself looking at purchasing a better interface if that one is limiting your workflow.  

Why don't you get Roland V-Studio 100? It wil solve all of your latency problems. It's portable too. You can record with it anytime and anywhere. I've been using Echo Audio "Layla 24/96" PCI sound card for years. After upgrading to Sonar X2, and applying some serious CPU intensive VST plug-ins I started to have big latency problems. No matter what I tried to do nothing worked. Constant dropouts, pops and clicks. So it was time to move on. Bought Roland V-Studio 100 three days ago. Had some initial challenges to set it up correctly. After one day all is well, and old latency problems were gone like magic. Everything runs smooth and happy. And the quality of sound is awesome. Right now you can get it on Amazon for $100 less then regular pro music online suppliers offer. Believe me, you wan't regret this decision. I know, a great piece of gear costs money, but in the long run you will be very satisfied. And V-Studio 100 doesn't cost $1,500-$2,000 like some of those high end pro soundcards. They say "you get what you pay for" and you don't have to spend fortune to get a great sound coming out of your monitor speakers. BTW, I do not work for Roland. Found out about this great piece of gear by reading ........ Amazon's castomer reviews!