The 1210i charger is just that - a charger. You could charge lipos directly off it with nothing else if you wanted to.
All a balancer does is monitor each cell and apply a small load to leech some of the voltage off the higher voltage cells. When you hook the LBA10 to the charger via the little feedback cable, it talks to the charger and probably reduces the charge rate if a large imbalance is present. You don't
need the feedback cable - it just makes it a more integrated solution. I use the LBA10 with the older EOS 7i charger and it works fine - just no feedback.
The LBA10 only has one balance connector input. So, if you want to charge and balance your two packs in series (as one pack), you are going to have to make an adaptor cable, something like this:
I made the leads long so I can charge the packs while they are in my Liposack and still have some wire slack. This cable allows the LBA10 to see both packs as one 4s pack. It's not very difficult to make, but you MUST make sure it is done right or you could burn up one or more of the balancer wires. Also note how the cables are zip-tied together in the pic above. This is so I hook up the cables correctly - if I hook them up wrong, I would burn up a wire.
The diagram at the very bottom of
this page shows you how the balance connector is to be wired. If you feel at all uncomfortable about doing this, you should have the adaptor made, or simply charge each pack seperately (takes twice as long to charge though).