Timing issues?

Possibly the PDC or FX buttons at the top in the toolbar.These are used to offset for latency issues during recording, but should then be disabled upon playback. that's the first thing I look at, 'cuz I need it for recording all the time, using guitar rig plug.
 

I own the us1641 which I believe uses the same drivers,  and actually gave up on it because of the drivers and weird issues. I through my hands in the air one day and ran out and bought the Scarlett 6i6 and all my problems went away immediately. 
It works great for live recordings of bands and what not,  but just goes off when trying to work with soft synths and any small amount of plug ins. 
 
Mr Anderton just announced in a thread here today that Tascam is totally aware of past issues and has taken the issue seriously finally ( too late?) and will strive to improve the drivers for their products . 
 
Anyhow for now if the fractal axe has a line output you might want to use the line inputs.
When tracking always turn off all your effect bins to avoid latency. 
Do not use the input echo, use the Tascams well designed monitor system
I would set the input/computer blend control about 12 o'clock so as to blend the playback from Sonar with the input signal. 
The headphone output is a little weak so it always ended up at full. 
The Monitor knob was handy to shut down the live monitors in the room when using a mike. 
 
Nothing special to do in Sonar just select the input , set the level just under peak and play away. 
Make sure you using ASIO drivers. 
Use the normal latency setting for tracking. 
I used 44.1 and 24 bit
It's too bad the drivers can't cope with the software as the hardware is real good quality for the money.