SC5000M PRIME
Long mixes won’t play from player 2 if USB card is inserted from player 1 or vice versa.
Songs that starts off slow or without beats, the SC5000M sets it to wrong BPM and when I hit the SYNC button, the platter stops spinning.
How do I edit its tempo manually or do mass batch BPM scan ?
All that You write is already known.
Regarding Your problem nr 1. Tracks that go via link if I remember can be max 270MB for now.
Regarding problem 2. The bpm algorithm is beeing worked on, so it needs some time. Will improve in one of the updates.
Beatgrid can be adjusted in Engine Prime software for better accuracy, than the player.
I can see you are new to the forum, so Welcome to ‘the family’ 
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As NoiseRiser points out, those issues aint new, but wellknown - for now you will need to edit the BPM in Engine Prime. (you can move the beatgrid on the players, but if the tempo is wrong, then you’ll have to go to Engine Prime.)
Denon do have focus on the BPM-thing at this time., so hopefully they soon will (1.) give us the option to edit bpm on the players and (2.) get Engine Prime/ Engine OS to do a better job analyzing those files.
Welcome again 