Avidemux error : Some tracks are used multiple times

[Hitesh12]

First some info on what I'm trying to do.
There is this HD file with a 5.1 ac-3 audio. What I want is to copy the video as it is, also copy the 5.1 audio as it is, but also create a stereo 2.1 (default) copy of the audio. In short - Same video and 2 audio - Stereo (default) and the original 5.1

The problem is that I cannot select the same audio track twice (see attachment).
The first one is aac stereo and the second one is a direct copy.
So how do I do this ? Why can't the audio be used twice ? I mean it is like making the copy of the audio and converting it into stereo, isn't it ? (noob here )

I also tried using mkvextract. Extracted the audio and then used it avoiding the repetition of internal audio. Didn't get any error but the audio wasn't in sync (when the source was the extracted audio). Plus it takes a lot of time as there are a lot of files to be converted

[Baldrick]

I can't see any attachment?

But I don't think the audio can be used twice in avidemux.

[ndjamena]

I'm thinking MakeMKV, but there are a hell of a lot of other options besides AVIDemux.

[Hitesh12]

I can't see any attachment?

But I don't think the audio can be used twice in avidemux.

Oops missed it
Have attached it now

[Hitesh12]

I'm thinking MakeMKV, but there are a hell of a lot of other options besides AVIDemux.

Ok will try that and get back to you
EDIT : There is no format converting option. It is mainly to save videos on dvd in mkv. Any other option that comes to mind ?