I’m not familiar with that seedbox provider, but unless you have a virtual private or dedicated server then you’re limited to the applications the host has made available.
If you do have a private node with root access, then you’ll be able to install whatever you like. Generally, these are limited to a command-line interface, in which case you’ll need something like soulseek-cli, but higher-tier hosting packages often support remote desktop which would allow you to log in and install the graphical version of the app as normal.