Freebase Dali

Use your Tascam for all the inputs. Your guitar and bass will be plugged into their own channels on that. (You will have to put the gain pretty high for those channels if you're going direct in, because there's no amplifier)

Once that's all plugged in, plug in the midi out from your keyboard and put it into the midi in of your Tascam. It should relay the midi messages to the computer.

In Sonar, create audio tracks for your guitar and bass, and set the input and output for both. The inputs will correlate to the inputs on your Tascam, and the outputs will probably go straight out to your soundcard by default. Usually it's a good thing to open up the console by going to View > Console, and on the right side of the rightmost white bar, right click the space and add a new stereo bus. Name it MASTER by doubleclicking the "bus 1", then set the output to your Tascam's first set of outputs that are connected to your speakers.
You'll also need to insert a synth of your choosing to be controlled by the keyboard. When you insert the synth, make sure you tick ON the option for "midi source" if I remember correctly, so that it automatically creates an audio track above the midi track, which is where the actual audio from the synth will play on. This will save you from having to manually set the midi track to output to a manually added audio track and having to set its input.

Set the midi tracks related audio track's output to the master bus you created. (Or, alternately, create a bus for each element which all output to the master bus, and output your actual tracks to their respective buses. This is preferable when you're dealing with multiple tracks that need to be on the same subgroup, like guitars, vocals, drums, synths, etc. This allows you to effect them as a group without having to do so individually for each track. Also makes it easier in the mixing process to control levels on a group basis.

On the midi track, the input needs to be set to the midi represented by your keyboard. It defaults to Omni, which means the midi data will be extracted from the host itself, like if you wanted to use the piano roll to create the notes. Since you want to use your keyboard, you'll need to select whatever representation there is for your keyboard, or your Tascam's midi out. I don't know what you'll see here for your setup. It varies.

At this point, you should be able to use your keyboard to send midi data through your tascam and into the midi track, which triggers the synthesizer associated with it, which outputs sound to the audio channel associated with it. It's a pretty logical flow, and everything works this way in Sonar.

For your audio channels, you should be able to play the guitar and bass and those low-level sounds should be audible on their respective tracks if you correctly set the inputs for those tracks. At this point, you simply add your amp modelling program into the plugin section of the track, whatever it may be, and your basic direct-in sound will be affected by it as it passes through the track.

Again, latency will be your biggest enemy here. If you're getting an unplayable delay, you need to ensure you're using the best driver mode for your system (located in the audio settings) and the lowest buffer size. The trade-off here is that the lower the buffer size, the better the latency, but the performance is a lot worse. Higher buffer sizes = better performance but higher latency. Considering this, you want to make sure that you're recording your guitar and bass very early on in the project when there are minimal amounts of active plugins and other tracks going. Also, not having a sh*tty computer really helps a lot.

As far as programs to use for synths, Sonar comes stock with plenty of them. I would suggest Dimension Pro for your pads, atmospheres and a lot of other stuff. Session Drummer is self-explanatory, but works the same way as any other synth does in terms of setup. Rapture is good for electronic leads and stuff like that.
If you require more, just make sure you acquire software synthesizers that have a VSTi version, and add the .dll to the main VST directory for Sonar, which is invariably located in "installation drive letter"\program files\cakewalk\vst plugins
This may change depending on the bit version you have, but it should be obvious where the correct vst location is simply by going to it and seeing the plugins that come with Sonar.

Not sure if this answers your question, and I usually try to structure things better, but I'm in a hurry and I'm not completely sure of where you're stuck.

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