A lot of people have this issue. I've used a lot of different DAWs and never encountered this problem before, ever! The mix in S1 sounds good, the kick knocks, the samples are in the position I want them to be, everything is clear. Nothing is on the master bus and I'm only using stock FX with S1 prime. When I import the mixdown back into S1, sounds the same as the mix. No issues....
However, if I play the mixdown on WMP, VLC, iTunes. put into Audacity, Sound Forge, or ANY other program, the mixdown sounds like someone has over-compressed it and the positioning of the instruments (stereo image) changes A LOT. The mix lacks clarity, feels like someone has sucked out 475hz with a WIDE Q, and the kick sounds fluffy. Again, never had this issue on any other DAW, and I'm not the only one.