Thanks for the input and references. I was able to configure my spectrum analyzer along the lines described by the link and see more than my orignial setup. I still need to put together a two tone tester - they're suggesting 1000hz and 1750hz.
I did make one intersting observation though. When I talk loudly into the microphone, I can see distortion products 10 or 20 khz away - that's without the amp running, just the 726R. The 726R has a pretty agressive ALC that does a pretty good job when it has time to react. Quick, large excursions allow distortion before the ALC can react and back off the gain. With a two-tone tester, the transceiver ALC should be able to ensure that the signal coming from the transceiver is clean - maybe
Then any distortion products should be coming from the amp.