Rich, while I love the trash cans, I find the iMac 5k to be superior in just about every way. I wouldn’t recommend buying new Mac Pros till they are upgraded.
Instead of USB cables and old monitor cables, run ethernet with 10GBe for server connections – I bet you already have those run anyways. Apple TV’s to your plasmas, or Blackmagic thunderbolt mini monitors. You’ll want a Netgear 10Gbe switch, Promise TB2 lighting adapters. and card to connect the switch to the server over PCI.
For wireless solutions I recommend a new Airport Extreme with wireless ac to maximize the speed of streaming to Apple TVs. Any mac could screen share to any apple tv enabled Plasma.
This solution gives us server connections of about 800Mb’s read/write over SMB. The old towers are still great for running as a server.
Bob Zelin can help you with all of this.
John Davidson | President / Creative Director | Magic Feather Inc.