Not exactly an obvious choice ... but Microsoft Office Visio does a great job at almost any type of graphical charting project. The canned shapes & connectors are easy to modify for whatever your specific use requires.
I haven't done any rack layouts with it but I can't imagine that it would be too difficult. As an example of how flexible it is, here is a channel strip layout that I did with Visio (it took a few hours to get the specific details down, but a course layout takes much less time). The quality is a bit off because of the 100K filesize limitation, but I think you can get an idea of the possibilities.
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