Same problem here, also running the Revising patch. No solution yet.

I'm not using the patch and the NPC voices are almost inaudible above the sound fx. I barely heard Olivia say to turn left at one point but otherwise I just drove off cliffs til I found a path that didn't end in a cliff. It really needs an option for adjusting voice volume. Rather odd that it doesn't.

It's not low. It's all over the place. Listening to NPCs in the station is very inaudible, even when going to their faces. A few meters further, you hear some other NPSs (above the fighting ring) just fine. The audio guy was a hack.

Man, if that's were the only problem with this game. I started to play it because of the glowing reviews on GOG, and stopped because I couldn't deal with the constant mouse acceleration you can not fix. In a shooter this is a death sentence. On the console with a controller this was alright I guess. Also: Why do we get bad quality video sequences. The one in Advent Behind The Scenes_compressed.mov clearly look better than the ones on the screen. And what's up with the constant black bars? This is a game. I could not walk to a hole in the wall, but when I switched from 1st to 3rd person view, it worked. The camera movement is taken straight out of someone using the Unreal freeroam-camera you have before you enter a level (you know, that which snaps in place every odd pixels). I'm guessing the ones giving glowing reviews have played the console version. Life is too short to bother with half-assed ports.

edit: ugh. i'm not sure exactly what's going on, but dialogue volume is somehow tied to FX volume. you can easily test this:

set FX volume to 100%, then start a new game: a conversation immediately starts, but your spacecraft sounds way too loud.
now, go to audio options and set FX volume to 0%, then return to the game: your spacecraft makes no sound anymore, but there will still be dialogue, as you'd expect..
now, without changing any settings, restart the level: as expected, you will hear no FX.. but also no dialogue!

so i assume that every time a load happens, dialogue volume will reset to your FX volume..
in this case, you could set FX volume to 100%, re-load, and then turn down FX volume again. but this is obviously incredibly tedious..

what's even worse however, is the negative mouse acceleration. :-/
it looks like it's the same old joke where a console port uses the code that was used for controllers, for mouse input. a lazy copy-paste.
but, well.. at least there's no dead-zone. right?
edit: it looks like this cap is only applied to the X-axis, not to the Y-axis. unfortunately, the X-axis is the more-important one.

this is really saddening, because the game starts off so cool, i was proper hyped..