Hi,
The problem is that, if you define a default rotue, only one default route can be active at a time. Although you can have two default routes, but only one will be active. You have to either use OSP between your ADSL routers and PIX , or try to use split up your default routes
something like this
route outside 0.0.0.0 128.0.0.0 NEXTHOP1
route dmz 128.0.0.0 128.0.0.0 NEXTHOP2
by using above ip addressing scheme we have divided the whole internet address space into two portions, although it is not very efficient way of doing load balancing, but atleast to some extent it is usefull.
Thanks
Nadeem Khawaja