Folgende vHost-Einstellungen führten bei mir zum Erfolg:

# Sample configuration for proxying an installation of EtherPad for Apache 2 
# The configuration should forward the domain requests to the EtherPad server running on port 9000 on localhost 
# See these instructions to setup EtherPad on your server: http://pauleira.com/13/installing-etherpad/ 

ServerName www.domain.tld 
ServerAlias domain.tld 
ServerAdmin admin@domain.tld 

ProxyRequests Off 
ProxyPass / http://localhost:9000/ 
ProxyPassReverse / http://localhost:9000/ 
ProxyPreserveHost on 

Options FollowSymLinks MultiViews 
AllowOverride All 
Order allow,deny 
Allow from all 

ServerSignature Off