UDP loss will always impact VOX. If you see the message about the game losing UDP and switching to TCP, there is packet loss occurring on the connection between you and the servers. The message is pretty drastic as the game does everything it can to maintain a healthy connection to the servers, but it cannot overcome Internet related issues.
The best way to determine where or if any packet loss is occurring is to run Ping Plotter to 206.16.60.38 and see if it shows any packet loss. This is best done immediately after a connection issue occurs.
If no packet loss is occurring, then kick down the resources, as I stated before, and see if the problem goes away. One of the most common problems I deal with is people thinking thier computer can handle the game, at max graphic settings, because they run some other very pretty game without realizing the measure of the demands a game can place on a computer is not only how it looks. The visuals are only part of the load and most of that load is on the graphics card, not the rest of the computer.