What version are you guys running?
Go into the options and click "Check Ports" and make sure it is working, you may need to change your port.
Make sure you have either UPnP or Nat-PMP enabled depending on what your router supports
Also try using it with the built in firewall on OSX disabled (Options > Security and Privacy > Firewall) or make the proper exceptions
I'm using Soulseek 2017-2-25 on OSX 10.13.6 High Sierra on multiple machines and confirm it is working fine (With all my ports properly configured).