But I don't get why you use 4 ip-adresses in 4 different subnets in your active-active example. XenServer 6.1 doesn't seem to support 2 IP-Adresses per interface by default.
Why dont use 4 adresses in 2 different subnets for example, e.g. 192.168.21.99 for target0 & bond0 192.168.21.100 for target1 & bond0, 192.168.31.99 for taget0 & bond1, 192.168.31.100 for target1 & bond1?