Get an MRF-300 to go with your MX-850. Using the MRF-300 you can put an emitter on each tv and send the commands for that tv to only the right tv. Set the left tv to port 1 and the right tv to port 2. When you select TV1 (left) the commands for that tv will be sent RF to the MRF-300 and the 300 will then send the tv commands only out port 1 and to the right tv. Same for the right tv, it will also send commands RF to the MRF-300 which will then be sent out port 2.
The MSC-400 is a great choice if you want to spend the money. It seems like a little more than you need for that application, but there is nothing like being ready for the future right? I love the MSC-400 they work great and are worth the money if you're a "power user" you will really apppreciate it.
If you really like toys you may consider the MX-3000. We use the 3000 in systems where there are many multiple devices so it is easy to customize and make it intuitive so anyone can pick it up and use it.
There are 10 types of people in this world, There are those who understand binary, and those who don't!