DAM scalability

I assuming you are asking about spreading DAM authoring across multiple servers, and not publishing. The performance aspects of spreading authoring of DAM across multiple servers are really not related to DAM so much as they are to how you cluster. If you are specifically worried about DAM performance one of the options (in 5.6.1 - this option isn't available in earlier versions) is job off loading of the DAM workflow processes. Depending on your usage profile DAM off loading may allow you to limit the numbers of CRX nodes you have in a CRX cluster. You can read about off loading here (http://dev.day.com/docs/en/cq/current/deploying/offloading.html) and clustering options here http://dev.day.com/docs/en/crx/current/administering/cluster.html.