So I have two comments:

If you are using Load Balancing etc for the web servers and an external SQL Server, all you should need to do is make sure both instances are pointing to the same SQL DB on the same SQL Server.  (I am assuming your solution is already doing file replication)

If you are looking for true redundancy, you should have the SQL Server (and its DB) clustered on a cluster server. Otherwise you still have a single point of failure, SQL Server.

The problem with the web farm document is that you already have to have a web farm.  And in fairness, configuring a web farm really isn't a DNN function, it's IIS and Networking.  The diagrams in that document are simply examples, and don't cover every situation, or even a recommended situation.

A web farm is really only a set of web servers, where a request can be served by any of them.  You can use NLB, clustering or a third party load balancer, all of which don't know about or care about DNN.  And for the most part, IIS doesn't care about the web farm either.  You might check general networking and Windows admin resources for load balancing and server farm setup, and the www.iis.net forums for working with IIS.

Jeff

ok, thank you, i will do some research on this.