If your users are unable to connect to DirectAdmin on port 2222 due to firewalls or proxies. It is still possible to setup apache to allow DirectAdmin to run through apache using its proxy options.
Just add a domain, or sub-domain as a regular domain to your account, and on a page for Httpd.conf Customization find and open for modifying your virtual host. And in text-area add the following lines:
ProxyRequests Off ProxyPreserveHost Off <proxy *=""> Order deny,allow Allow from all </proxy> ProxyPass / http://server.example.com:2222/ ProxyPassReverse / http://server.example.com:2222/
Just replace server.example.com with actual hostname of a server powered by Directadmin.
Note that you will likely need to shut off the Referer Header Check for DA versions 1.34.5 and newer.