Well for 12-15 users, all you need is a 100DCD (100D w/CSU/DSU if Legend) and 016MLX or 016T/R or 024TDL (Magix only) to network the switches together. Then if you add an 800 GS/LS, you could get 1 line from the LEC and there is your 911 access. Cost isn't that high for the Processor, 100DCD and digital/analog ckt pack. It's the stations that will add up. Realistically, you could probably find refurb Legend stuff that will be cheaper than the DSU and mux solution you are thinking about. Ballpark...I think you could put this solution together, with refurb equipment including digital stations, for about $5k-$7k installed.