Yeah, but what you want doesn't exist. Kinda like what's happening with business phones, they are all going IP now. They cost twice as much as the old analog or digital but soon they will be your only choice. Not real great to hear if you need a couple of hundred.
-Hal
Phone systems are changing. Over all cost is coming down, if you look past the old school “big names” They are use to selling VERY expensive head units and reasonably expensive phones. Now a phone system just needs a low end server and some network switches. Intercom is taking the same route. I have worked with the Bogen and Simplex systems. The Simplex is similar to what the OP is talking about. I think it is over priced junk, but then that could also be the fault of a sloppy company getting all the local installs about a decade or two ago.
Very high channel count and density is easy, nothing more than an IC with a heat sink now. However the cost to home run “special” cable drives the cost up. Inflexibility of such a system is also a big problem. The cost of VOIP is dropping very fast. If I were specking a system that needed individual control like that I would jump right to VOIP. Any modern building is going to have a network system any way. Just build communication into it directly. In the long run the cost is lower.
As for volume per room they already have speakers with volume controls build in. All those problems have been solved for 30+ years.