I also have the same problems.
I have a 3200x1800 Yoga 2, and have loved musicbee before, but now i cannot use it at all.
http://imgur.com/TJxnmf6(The following is the standard Musicbee, just updated, I did however increase the size of all the text from 9pt to 11pt otherwise it would be extremely hard to interact with.)
The playback buttons and other buttons are unusablely small.
The window buttons are crammed into the edges of the screen.
I have been able to find workarounds to most applications on my new PC to make them look okay, except MusicBee and VLC, both of which have unusable playback buttons)
Thanks