When you export dxv on Adobe Media Encoder using Quicktime, don't need to set the specs for every file. You can make a preset and just drop it.
Those presets have the ability to take parameters from source file and match it.
The 'Match Source' option is something we wanted to add from the beginning as well. But somehow we did not yet get it to work, we have a ticket running at Adobe to help us out. So hopefully we can offer the 'Match Source' option in an upcoming version of the exporter.