Yeah this is an issue for me on PS5. It uses the rear surrounds for dialogue in 5.1/7.1 and with DTS/Dolby/PCM.
It seems to just be a problem with ME1 in specific, ME2 and ME3 sound fine.
Some Reddit threads about the issue:
https://reddit.com/r/masseffect/comments/nbxxnq/_/gy2caws/?context=1
https://reddit.com/r/masseffect/comments/nbxxnq/_/gy2bdfl/?context=1
I am unable to get Mass Effect 1 to output any audio out other than my left and right speakers when trying to output 5.1 audio. Mass Effect 2 and 3 work fine but 1 is only giving me stereo. I have hdmi hooked up to my receiver. Does mass Rffect 1 still not have surround sound support? Could never get the original games surround sound to work either. I would assume with this major release it would have working surround sound.
