|I'd never heard of EMS until my curiosity was piqued by the OP, although I know that some servers have service processors that allow serial or net access to the boot process.|
I'm still not quite sure why anyone would need serial access. The only scenario that I can think of is a remote server where there is a possibility of network access failing. When I managed that sort of scenario I always made sure that there was at least one person on-site that I could trust to follow instructions over the phone.
I'd be fascinated to know why the OP has this requirement. Let's hope he follows up on this topic. So many people never do, which is a real drag.