Ok. I have all the sites working, though not exactly how I had planned.
Problem 1: All redirecting to client9
Solved: Removed the multiple IPs. Everything now uses * and clients no longer have the ability to select a separate IP for their site.
Problem 2: When everything was *, client 9 was redirecting to some weird location.
Solved: Client9 had an entry in their .htaccess file to automatically add 'www' to the front of their domain. ISPConfig had been set to no leading 'www'. ISPConfig won. Since the client hadn't set up their site to respond to non-www URIs, it failed.
I'll figure out what went wrong with the multiple IPs on the system at a later point.
Thank you for your help.