WaveWorld is free but not public domain. Many of the files are sampled from commercial synth presets, which is a bit of a grey area. It's okay to use those samples in your music (also commercially), but if you want to be 100% certain that everything you use is in the public domain, they are the wrong choice.
But my main question is, does anyone know about the copyright status of the samples WITHIN the Unreal II PM s3m by Purple Motion? I'm particularly interested in using the piano chord samples within in my own work.
That's a particularly tricky file to ask about because it contains samples from movies (e.g. "ten seconds to transmission" from Batman). Many remixes (in particular those that ended up on CDs) of this song have avoided using those voice samples due to the lack of copyright clearance.
The rest of the samples are certainly also not in the public domain - unless someone specifically says so, you cannot assume that this is the case. Most artists will not care if you use their samples, as long as you credit them, but in many modules those credits are missing so often the wrong person gets credited when yet another person reuses a sample. Some of the samples in Second Reality are certainly original, while others are taken from other modules.
Again, if you absolutely need to be sure you are only using public domain material, this is not the right way to go.
For the specific samples you asked about, they are sampled from the famous Piano 16' patch from the Korg M1 which is heard on thousands of records and modules of the 90s. They can easily be recreated with Korg's M1 VST plugin in higher quality if you want a version that is guaranteed to not "belong" to anyone - although again, sampling synth presets is a bit of a grey area but noone ever got sued for sampling a single patch, it gets more problematic if you e.g. sample all the presets of a synth and then sell your own sample pack based on them.
I have attached some high-quality recreations of those piano samples to this post. They are directly sampled from the Korg M1 VST. As far as I'm concerned you can use them for anything you want, but again - they are based on commercial synth presets, which means that they are free to use, but not in the public domain.
