Whats the bandwidth of each ADSL link? Is it not easy to get a single big fat pipe or 2 pipes for redundandcy purpose instead of having 6 of them? That would definetely make life easy with management and when thinking off other capabilities like load sharing etc.,
i think firstly -- might be a bit of a problem to connect 6 adsl lines to one 2611xm , theres only 4 wics
so lets say you have 4 adsl lines and want to load balance ,
one way to do it would be via 'multilink ppp' -- you have to discuss this with your isp because they will have to set some configurations on thier side , but essentially all the dsl lines will get bundled and you will essentially have one IP for the bundle , similar to a layer 3 etherchannel, except not as good.
this is one method thats easy to set up and works reasonably ok, i believe there are other ways -- best to involve your isp in the discussions.
if i was in your position, i would cancel 5 x dsl lines and get a decent connection like an E1 or Les 10 from your isp , and use the remaining dsl as a backup.