How do you encode to 448kpbs ac3 with avidemux?

I have some mkvs with aac 5.1 audio and avidemux seems the simplest solution to me to convert to ac3 5.1.

However it only goes up to 384kpbs.

How do I set it to 448kpbs in avidemux?

I just finished one to 384 but I'd like to do it in 448kpbs.

Please let me know. Thanks.

FYi I did try eac3to but it asks for nero audio decoder 2 and I don't have that. And I don't want to install nero for just a decoder. If however I can just download the trial and then copy the decoder I would do that.

Thanks.

Edit - fyi I'm just doing the "copy video" and just encoding the audio.