Which GTX cards do you use and which render codec do you use? Also note that Vegas does not take advantage of SLI or Crossfire. The only time I managed to get two GTX cards to improve render times was with two GTX570 cards which MUST NOT be set in SLI and the card in the second slot MUST be set for GPU acceleration under preferences.
Use 2 GTX 570. 1Gainward and 1 MSI, both 570 with 1280MB of memory. Ok, then off SLI and in Vegas preferences imposed n. 2 for video processing. How to use the MainConcept AVC codec. sorry for my bad english
In Vegas Pro 14 you need to enable GPU rendering in the internal preferences. Hold <SHIFT> while clicking Options > Preferences. On the "Internal" tab click search "GPU" and set "Allow GPU Rendering" to TRUE. Then a new "Encode mode" option will appear at the bttom of your MainConcept and Sony AVC render customs settings.
Why would MAGIX have had the GPU enable in the Internal Menu? Are they protecting us from all the confusion and angst that has appeared over the last, what, five years?