Hi,
In order to fix a lot of other security related bugs Net Balancer is trying to remember source and destinations IPs and use same gateway for a pair.
In your case, Net Balancer will not help. What you need is to create a bond between 2 ADSL.
If your ISP provider doesn’t support bonding then another option is bonding over VPN, but that will require another server to VPN into and bond that 2 VPNs