[CentOS] IPv6 address configuration and default IPv6 address with CentOS 6.8?

Hello,

when I have this in /etc/sysconfig/network-scripts/ifcfg-eth0

TYPE=Ethernet
NAME=eth0
NM_CONTROLLED=no
ONBOOT=yes
DEVICE=eth0
USERCTL=no
...
IPV6INIT=yes
IPV6ADDR=2001:DB8:DEAD:BEEF::10
IPV6ADDR_SECONDARIES="2001:DB8:DEAD:BEEF::20 2001:DB8:DEAD:BEEF::30 
2001:DB8:DEAD:BEEF::40 2001:DB8:DEAD:BEEF::50"
IPV6_AUTOCONF=no
IPV6_DEFAULTGW=2001:DB8:DEAD:BEEF::1
IPV6_DEFAULTDEV=eth0

I have a virtual server, and there are the alias addresses splitted,
e.g. IPv6 2001:DB8:DEAD:BEEF::40 is used by BIND (named, authoritativ 
DNS server)
IPv6 2001:DB8:DEAD:BEEF::30 is used by MTA (postfix, DNS has this for MX 
of this domain)
IPv6 2001:DB8:DEAD:BEEF::20 and 2001:DB8:DEAD:BEEF::10 are used by 
Apache (httpd)
...

and this is also splitted in the firewallconfig ip6tables

-A INPUT -d 2001:DB8:DEAD:BEEF::30 -m tcp -p tcp --dport 25 -m state 
--state NEW -j ACCEPT
-A INPUT -m tcp -p tcp --dport 25 -j DROP

-A INPUT -d 2001:DB8:DEAD:BEEF::40 -m tcp -p tcp --dport 53 -m state 
--state NEW -j ACCEPT
-A INPUT -d 2001:DB8:DEAD:BEEF::40 -m udp -p udp --dport 53 -j ACCEPT
-A INPUT -m tcp -p tcp --dport 53 -j DROP
-A INPUT -m udp -p udp --dport 53 -j DROP


where can I define which IPv6 address is used as source IP, when doing
e.g.    wget ...
            ssh ...
            ... | mail test at example.com
            ...

Thanks,
Walter