Make sure you don't have any of your admins you're trying to move to the new group(s) in your default gmod/settings/users.txt file.
I believe our ULib ACL reads that first, then imports from there. This could cause conflict if you edited that manually, then tried moving/changing the other people you're wanting to add.
BEFORE editing the groups.txt manually (and if you already have, move it/delete it from /data/ULib, restart and let ULib rebuild it)
Use server console or game rcon to create the groups.
ulx addgroup advadmin admin
ulx addgroup magicadmin advadmin
ulx addgroup userplus user
(Think that covers most of yours)
Then restart the server.
Go and see if the groups.txt file now at least has your new groups, minus the allows/denies of course, and the redirected inheritance of the default groups.
If that's proper, then start adding your redirected inheritance, allows and denies.
Megiddo/SPBogie, I've not dug deep enough into ACLs, our code doesn't force superadmin/admin/operator inheritance does it? He's redirecting superadmin and admin inheritance, which in theory should work, but I'm not sure our ACL accounts for someone wanting to do it.