click audio/metronome

The metronome (by default) goes to its own buss which then outputs to "Master." If your interface supports multiple outs, you can change the "Master" on the metronome buss so that it is feeding into another (monitoring) path. To use the metronome within SONAR, you would need to break that routing chain from the metronome buss to keep the signal from passing into the master output. You may need to reference your interface manual as the new output path may then be hard-wired to a specific output on the interface by doing this.

I don't see an audio interface in your signature so like mettelus say's it depends on your audio interface output count. If you have 4 outs then it's easy. Just send the metronome to 3/4.  If you only have 2 then you'd have to split to left /right. ( edit:  I see we posted same time ) 
I play as a solo act and also we have an acoustic duo. 
I've always used a stereo backing track with Drums, Bass and sometimes a little keyboard.  
But our acoustic duo we didn't want anything but the Bass player to be heard by the audience so I used a left /right split. 
 
The drum track we put to a powered floor wedge and the Bass track I sent to a small Bass amp. It worked amazingly well. Because the Bass amp was behind us it really kept us on track. The drum track in the floor monitor was kept at a low level. We could hear the count in but once we started the drums were pretty subdued. The audience never heard them apparently. Friends were coming up afterwards and asked how the heck we had the bass happening. It was not obvious to most. We are looking for a real bass player but this is working so well we have stopped worrying about looking.   
 
This is my live set up      http://www.cactusmusic.ca/johns_rig.htm   
 

So I see your interface is only 1/2 output. 
I'm just using the laptops 1/8" mini jack most times and it's always worked fine. Certainly never crashes. I also use this cheapo Behringer RCA output interface that uses MME drivers and seems stable. But there's really no sound quality issues with the on board audio.
Some laptops hum but mine is real quiet.
The USB connection to the PA would not work because it can't be split to your monitors, the audience will hear it.  

I don't seem to be able to get at the Bose Web site, it must be down. But a friend of mine had the same system and if I'm correct the USB is for a stereo send from a computer. 
It could be sent left or right but I'm not sure it's input has a AUX send as well. 
This would be the critical factor. 
The USB input will need to be able to be split left and right and not only that, but then only one side would need to be sent to the AUX. Not many mixers can do this on one stereo channel strip. Like other mixers you'd have to use 2 mono inputs to do this. 

Cactus Music
I don't seem to be able to get at the Bose Web site, it must be down. But a friend of mine had the same system and if I'm correct the USB is for a stereo send from a computer. 
It could be sent left or right but I'm not sure it's input has a AUX send as well. 
This would be the critical factor. 
The USB input will need to be able to be split left and right and not only that, but then only one side would need to be sent to the AUX. Not many mixers can do this on one stereo channel strip. Like other mixers you'd have to use 2 mono inputs to do this. 

The T1 DOES have an AUX which I've assigned the drum track to - so it's panned, muted & things are proper live - I can bring drums in & out of mix - faintest of "whoosh" noise from drums in background of the other instruments channel(I could live w/that BUT...I save the song...& come back to it later & the drums are right back where they don't belong -I'm done w/this for now, gonna borrow a bass & just go as three pc & forget the sequences (works better for my solo OR duo) - thanks for your attempts to help! I DO appreciate it