Photoshop CS6 worked with Media Encoder CS6 (version 6.0.2). It sounds like you're trying to use the current version of Media Encoder 14.2 with Photoshop CS6 and yes, that version will not work with CS6. If you do not have a time line, Render Video will be grayed out, If thing in the timeline are not sey proterly the tenokare neet to be address the checken coop oersinal car m encoder maume line are not prople set You can set a very low frame rate encoding youre video for there is no motion in the still images you want to display.
When you tried to create your slide show did you stack you images so the fit within your video frame size and create a video timexline where yoy displayed your image layers in some sequence. Here is what I see in CS6 export render video Here I set the frame rate to 10FPS to create a small video file for the web it rendered a 4MB size file. The media encoder should not be grayed out in the render video dialog. If you have that when you use export>Render Video. There needs to be a Time line that meat the requirement for the documents to be encoded as a video. You first need to solve the issue you have in you CS6 install where Adobe Media Encoder is grayed out.
You may need to install an old version of the medial encoder so the profile will be compatible in the CS6 Media Encoder subset. You may be able to install Adobe Media Encoder and create custom profiles you can add to the Presets included in Photoshop CS6. In the Subset of the media encoder built into Photoshop. You can not create your own custom Profiles. There is a subset of Adobe Media encoder built into Photoshop that include some Preset encoding profiles.