It appears as though there is no way to include the "Splunk technology add-on for windows" during a silent install of the v6 universal forwarder. Doing a silent install without this add-on throws the following error in splunkd log....
11-27-2013 12:47:49.171 -0500 ERROR ExecProcessor - message from ""C:Program FilesSplunkUniversalForwarderbinsplunk-netmon.exe"" splunk-netmon - NetmonConfig::InitNetmonConfig: No valid stanzas found.
Manual installation work fine and creates the typical MSICreated inputs.conf in the tech add-on folder instead.