This was mentioned above, but not sure of your situation. How difficult is it to change MIDI channel on your controller/keyboard?

Two tracks with echo on can be set to channel 1 and 2, then the channel output of the controller will tell which to play. Is this not viable for you?

When I get some time, I'll try these macro programs. Looks like it could be helpful, Craigr68. Thanks.
Re: the question by Mettelus: It's sort of responding to a question in another language, since I'm pretty deficient in music computer language. However, here is what I think I understand. My song has multiple tracks. During the song, I like to play a synth lead for some of the time, and piano for the rest of the time---alternating back and forth a couple of times. Though I have several hardware synths, both of the sounds in this song that I'm trying to play live are coming from the same (Kronos) synth. THus, the output of my synth is already set to the same output as both of these tracks--or, more specifically, I have set each of these 2 tracks to the output channel I always use on my synth. However, when I tried to click on 'echo on' on the track that wasn't highlighted at the moment (the highlighted track automatically has 'echo on' highlighted), this did not result in me being able to play the non-highlighted track from my synth (controller.)
Is that clear? Perhaps if I had highlighted both tracks using the control key as I clicked on each, this might have made them both responsive to my playing?
 
LNovik

Are both track use Kronos (hardware) synth? I guess there can be some misunderstanding. At least I have assumed that you use Kronos as a MIDI keyboard and have 2 Software Synth with 2 tracks.
So, what are exact Output settings for both MIDI tracks? And if both point to Kronos, how you expect Kronos recognize the change?
That is quite important: while MIDI tracks in Sonar have "Program" option, Sonar is only sending it when playback is started from the beginning. And there can be other explicit and implicit tricks, on Sonar and on Kronos side.

I am confused the same as azslow3 on your setup. The reason is this... *if* you are using the Kronos for both sounds (via external audio out), then the easiest method is to route the audio out from the Kronos to a single *audio* track. SONAR could care less what goes in, and all switching would be on the Kronos (no "mousing" required). Play patch one, switch patches, play patch two. NO MIDI is even recorded/required by SONAR for this (but also limits any editing, since no MIDI). You would want to save those patches as user patches so they are right next to each other on the bank listing.
 
Now, *if* you are using the Kronos as a MIDI controller (*only* sending MIDI (key note) data to SONAR), the best method is to set up two soft synths with both having MIDI input from the Kronos (MIDI only, no external audio in). Set one to MIDI channel 1 (or whatever), and the other to MIDI channel 2 (or whatever + 1). Manually input echo both tracks, then shift the MIDI channel out on the Kronos between "patches" and SONAR will shift which soft synth plays/records. Piano is fairly generic, and the lead can be something similar (and even edited to be final if desired).
 
For "real time" play, one of the two methods above would be simplest. Although there are methods to record MIDI and drive the Kronos with it, you will introduce latency, and cause routing issues that would take a bit more to explain. Also, the "switching" aspect would get complex *only if* you wanted to record the MIDI and the audio output. As it seems the audio output is highest priority, I would use the first method above. If you then get into a recording situation, overdubbing (recording one track at a time) would give you the best and simplest editing options.