Connect to a Cisco ASA for client VPN through Balance

We have had challenges with the Windows VPN client, specifically with L2TP encryption. What I would like to do is use our old Cisco ASA as our VPN server. If I have that on a local IP inside our network, how can I make WAN 2 forward those requests back to our internal Cisco? I have opened up about everything I can think of, but it won’t connect. I assume drop in mode or something? Suggestions?
(Balance 310 - 7.0.1 build 2988)