I haven't gotten back to this yet to try it, but can see from your
explanation that I wasn't doing it right. I was attempting to put in a
source and destination URL and copy the site directly to the new server. I'm
looking at the command help, and cannot figure out where I got the idea that
this would ever work.
Smigrate: Backs up or restores a SharePoint Web site.
Usage (backup): smigrate -w <website URL> -f <backup file> [-e] [-y]
Usage (restore): smigrate -r -w <website URL> -f <backup file> [-x]
The instructions couldn't be clearer. Thanks again for your help, and for
following up on this.