How to use omindex-produced Xapian database with xapian-haystack?

[Charles]

We are migrating an omega-based solution to Django, because we need 
authentication and authorisation.

We are developing a Django solution using django-haystack and 
xapian-haystack https://github.com/notanumber/xapian-haystack

I am stuck on making xapian-haystack read our existing omindex-produced 
Xapian database.

The documentation linked above includes ...

HAYSTACK_CONNECTIONS = {
     'default': {
         'ENGINE': 'xapian_backend.XapianEngine',
         'PATH': os.path.join(os.path.dirname(__file__), 'xapian_index'),
     },
}

... which is a single file but our omindex-produced Xapian database is 
several files

-rw-r--r-- 1 root root 4.4M Sep 28 14:16 docdata.glass
-rw-r--r-- 1 root root    0 Sep 28 14:06 flintlock
-rw-r--r-- 1 root root  141 Sep 28 14:16 iamglass
-rw-r--r-- 1 root root 572M Sep 28 14:16 position.glass
-rw-r--r-- 1 root root 522M Sep 28 14:16 postlist.glass
-rw-r--r-- 1 root root  44M Sep 28 14:16 termlist.glass

I guess this is more of a xapian-haystack question than a Xapian 
question but the mailing list and irc #haystack mentioned on 
https://github.com/notanumber/xapian-haystack are defunct