If there is Linux source, you might be able to port it to Chromium OS as a command line program. There are a few people that have built various utilities as add on packages, but I do not believe this will work for Soulseek, because they do not distribute the source code.
You might have better luck porting BitTorrent. Source code for the original client is available on SourceForge:
There are plugins and/or Apps that give you an interface to a BitTorrent server running on a remote machine, but I do not believe anyone has put a client/server on Chromium OS yet.