This should get you close. You may or may not want to turn the optimizer on, we found it caused problems with a couple of users' scripts. Also you may want to turn admin auth on and set a username / password (there's info on that at the XCache website). It's not really needed under mod_fcgid as the end user can only see their own cache if they upload the admin tools. Actually given that under mod_fcgid it's cache-per-process, they can only see their own cache for the process that they happen to connect to.
You'll probably want to tweak the xcache.size value too.
Btw you mentioned UnixyVarnish. This is a total aside, but if this is a shared server and you care about your users having accurate stats, and you care about billing them for the bandwidth that they use, you should know that any hits on the Varnish cache are not logged at all. Found that out the hard way with a customer pulling in 2 million+ visitors per month and north of 10 million page views. He was logging close to an 80% cache hit rate and none of that considerable bandwidth usage was showing up in his account. All of his stats were off too.
mine that have problem is a E5-1620 + 32GB RAM + Apache 2.4 + UnixyVarnish + FastCGI or SUPHP