This might be too little too late (it's been almost a month since this thread was posted), but If you're looking for a modern s3xmodit tracker, you'd be hard pressed not to go with Open ModPlug Tracker. A lot of work has gone into it over the past couple years and it's surprisingly good. So unless you're more of a traditionalist looking for a more classic mod editing experience, OpenMPT is a good bet. Otherwise there's MilkyTracker amongst others for a more traditional but still cross-platform experience.