Hi .. with 2 ASAs .. In you scenario I believe you could only have 1 option:
1.- configure a cluster between the 2 ASAs for VPN load balancing. The ASAs will be on single mode. No failover configuration. The cluster set up is supported on single mode only and it does need the devices to be forwarding traffic which does not happened on a failover Active/Standby set up. You would need 2 pairs of ASAs if you want VPN load balanced and failover Active/Standby.
http://www.cisco.com/en/US/products/ps6120/products_upgrade_guides_chapter09186a0080609cc7.html#wp1062453
http://www.cisco.com/en/US/products/ps6120/products_upgrade_guides_chapter09186a0080609cc7.html#wp1061864
below a brief explanation ..
" If you have a remote-access configuration in which you are using two or more security appliances or
VPN Concentrators connected on the same network to handle remote sessions, you can configure these
devices to share their session load. This feature is called load balancing. To implement load balancing,
you group together logically two or more devices on the same private LAN-to-LAN network, private
subnet, and public subnet into a virtual cluster.
All devices in the virtual cluster carry session loads. Load balancing directs session traffic to the least
loaded device in the cluster, thus distributing the load among all devices. It makes efficient use of system
resources and provides increased performance and high availability.
One device in the virtual cluster, the virtual cluster master, directs incoming traffic to the other devices,
called secondary devices. The virtual cluster master monitors all devices in the cluster, keeps track of
how busy each is, and distributes the session load accordingly. The role of virtual cluster master is not
25-6
Cisco Security Appliance Command Line Configuration Guide
OL-8629-01
Chapter 25 Setting General IPSec VPN Parameters
Understanding Load Balancing
tied to a physical device; it can shift among devices. For example, if the current virtual cluster master
fails, one of the secondary devices in the cluster takes over that role and immediately becomes the new
virtual cluster master "
I hope it helps .. please rate it if it does !!