adding IPv6 to an existing IPv4-only 'high-perf' nginx ... Pressflow web-stack?

(moved from http://groups.drupal.org/node/148319)

our current web stack is an all IPv4, DIY implementation of,

    nginx
        multiple listeners on IPv4:80, IPv4:443
        proxypass to varnish-cache on 127.0.0.1:9000
      |
      |
    varnish-cache
        listener on 127.0.0.1:9000
        filter/pass to 'faux-CDN' on Apache2
            'img' -> 127.0.0.1:12003
            'css' -> 127.0.0.1:12002
            'js'  -> 127.0.0.1:12001
            '...' -> 127.0.0.1:12000
      |
      |
    apache2/mod_php,mod_deflate +
    Pressflow6/memcached(cache_inc/session_inc/lock_inc)
        listeners/vhosts on 127.0.0.1:1200{0,1,2,3}

all works as planned.

we're now adding IPv6 listeners on assigned AAAA records @ each nginx "server {..." for dual-stack operation,

    nginx
-       multiple listeners on IPv4:80, IPv4:443
+-      multiple listeners on IPv4/IPv6:80, IPv4/IPv6:443

questions:

what other parts in the stack need to change to accommodate IPv6 and keep caching, Pressflow, etc working?

does each after-nginx component need a mirrored/parallel IPv6-only instance?

or, simply add IPv6 listeners to the current IPv4 listeners?

or, leave it all alone, depending only on the nginx proxy pass to correctly hand-off to the chain, regardless of the inbound address family, -6 or -4?