Calculate conductors for box fill
Reading your question, it appears you are familiar with NEC Article 310.14 so lets not get into that. The biggest problem I have ever faced with multiple wire and devices was not meeting the box fill requirements but getting all that stuff into the box and mounted properly. So plan how you are going to splice and connect all of your conductors carefully. Bundle all of the common conductors together, try not to crossover too many conductors and plan to keep your splices in different areas of the box and not interfering with the installation of the devices. 

One last thing, these boxes come in different depths, traditionally 1 1/2, 2 1/2 and 3 1/2. If it's not too late you might try to purchase and install the 3 1/2" variety.

Good luck.