Lowered volume after exporting in Premiere Pro

I have a 5.1-audio video. What I do in Premiere Pro CC 2017 (Windows 10):

1. Import the video.
2. Drag it into the timeline to create a sequence. A 5.1 48000Hz sequence is correctly created.
3. I export the video using the 5.1 setting for audio (usually PCM, but for compressed formats it doesn't help).

And, unfortunately, although the 5.1 track is successfully created, the volume is noticeably lowered, comparing with the original.

I also noticed that when I open Audio Track Mixer and click the play button in this window (Audio Track Mixer), it shows the dB to be on a level from -20 to -9. Even though all of the dB settings in the Audio Track Mixer are on 0 of course.

I may also add that I've experienced similar issues for stereo tracks in the past.

Thanks for the help!