7.1 channel audio problem

i have a audio file (mka) with 7.1 channel

when import to audacity ( import - audio ) only 5.1 channel imported

my os :windows 10 64bit
audacity v : 2.3.2
mka 7.1 file in movie format : ac3

i have not problem with 5.1 mka file

The additional 2 channels are [u]matrix encoded[/u] into the two rear channels the same way that Pro Logic surround was encoded on 2-channel VHS tapes.

I don’t know of any software decoders for that but the matrixed information should remain embedded in the rear channels unless you something strange to change the time/phase difference between those two channels.