Physically, routing is as simple as connecting line outputs of the Tascam to inputs of the ART, and outputs of the ART to line inputs of the Tascam.
As far as the software, the way things are named may vary, but you route send faders from channels (if using it in parallel like a reverb) or channel outputs (if using it in series like eq or compression*) to hardware outputs. For compression use you'll typically want to use the return channel fader (post compression) if there's automation involved.
Route hardware inputs to your master fader or a DAW channel of some sort. It depends on whether you want to render (/bounce/export) the final mix in real time or if you want to render it offline (as fast as the computer can do it).
To be able to render mixes offline you'll need to record the output of the effects unit to a new track in real time. But if you change things you may need to go back and re-record it in real time.
If you are okay with rendering in real time then you can just route the hardware input to the main mix bus or a submix bus.
*I think some DAWs have built in hardware effects loops that let you do this routing in a more direct way with a plugin. I don't know about Sonar.
Either way, hardware effects can add time to the process, and they typically don't sound as good as software equivalents. That plus the lack of undo and recall make hardware effects suck for use with DAWs.