Hi y'all.  After exporting tracks to MP3 from a mixed tune on X2 I notice the resulting MP3 file has a lower volume than the original and some distortion.  I have checked the track and master volumes and all seem within range (i.e. nothing peaking too high).  When I bump up the levels to gain some volume I gain some distortion also.  Thinking I may not be setting the outputs correctly or something ?  Appreciate any advice or tips from you experts.  Thanks.

Have you tested if exporting to WAV does the same?
Does the mix go through plugins or bus plugins or strange settings in bus or master volumen?
Does the mix go through the ProChannel with strange settings?
I would first check if exporting to wave hase the same behavior.
 

You mentioned you checked your tracks and master bus but what about your hardware bus ?
The master bus and the hardware bus are independent. Make sure your hardware bus is set to 0dB. that's important.
what are you using for an audio device ?