If the drivers are showing up as you mentioned at the Sonar Edit Preferences Audio, then your Sonar is recognizing the drivers for the Tascam 1800. Playback-Recording select ASIO. Driver Settings, Playback Timing Master, choose the main outs there, and choose 1/2 or whatever as Record Timing Master. Devices, check the appropriate ins and outs for the Tascam.
 
The Tascam 1800 has a gain knob for each channel, make sure they are on. It also has a signal knob for headphones or speakers, check that too. If you have sound at the headphone jack at the Tascam, you just need to select the track inputs at your Sonar track pane.
 
At the track in Sonar be sure to check the correct track for your input at the Tascam. The tascam might say something like 2L 2R 2 Stereo? anyway...these are in pairs, like 1 L, 2 R, 1-2 Stereo etc...for the 8 or 12 inputs it has. If you are plugging directly into the Tascam at 9 or 10, check that you are going Hi-Z and not Mic or line or whatever it has. If you have a mic, plug that into #1 at the Tascam and check that too. But you have to choose the input at the track input in the track pane, and arm the track to record to see if you have a signal there. Insert an audio track, choose the input your using, and arm the track to record and test it.
 
You can also use an amp with a DI or a DI Box to go into the XLR channels at the Tascam without using the HiZ at 9 or 10. You can go into a effects processor, equipted with a DI or to a DI Box and then into the XLR's. This is how I do it. I never go staright into a HiZ at an interface. I am assuming you are playing guitar as your picture shows? You can also run Amp headphone jacks into the Tascam. Some amps and processors have a DI built into them.
 
Don't use a USB hub for the Tascam, and do use a direct 2.0 port. Turn your Phantom Power off if you are running in a guitar at the Tascam.