Hi Californiamusic,
I use outboard gear all the time. Usually I just use the External Insert effect. Add it to your effects bin, set ins and outs, measure latency and you're done.
A couple notes:
1. If you put the EI effect on a bus it won't measure latency until you have signal routed to the bus.
2. It can cause some issues with metronome pre-count.
3. Sonar considers any ins and outs used in an EI as a stereo pair, even if you're only using one of the ins and outs. So if you use in 3 and out 3, Sonar will consider both 3 and 4 as in use and unavailable for use in other places.
Good luck,
Dean