wish: finer "auto passthru" selection

[Trillian59]

Description of problem or question:

Defining "auto passthru" for certain audio formats is a nice thing, but what I am missing from it is a more detailed way to define what to passthru and what to convert.
For instance, I like to passthrough AC3 5.1 tracks, but want to convert AC3 2.0 tracks to AAC (to save space).

HandBrake version (e.g., 1.0.0):
all, now on 1.3.2

[Woodstock]

There is a place listed for feature requests, and that's github.