@HaydenField000... it's possible to convert stereo to surround 5.1 via avisynth, using these filters (try them and choose one according to the results on your source):
UpAction() #action movies only
UpDialog() #dialogues mainly
UpGerzen()
UpFarina()
UpMultisonic()
UpSoundOnSound()
Once you have a 5.1 converted track, you'll just have to encode it using your favourite encoder, for instance, NeroAAC.
Sample script:
Code:
video=colorbars(width = 704, height = 396, pixel_type = "yv12")
audio=DirectShowSource("audio2.0.something")
#using WAVSource for .wav audio files is reccomend
#you can use FFAudioSource as well
audioDub(video, audio)
UpDialog() #it converts to 5.1
Please note that upmix it's not like a real 5.1 audio track, due to potential unexpected behaviours, 'cause it uses filters to detect frequencies and create channels, so you might have a light echo in FL and FR channels during dialogues, when they are supposed to be mute in a real 5.1 track etc.
Unfortunately, there is no magic and I really wanted to upmix audio tracks back in the days, but in most cases it's not worth it and it's better to just make a Loudness correction (Normalization, EQ etc).