@shadowking, I tried the settings you suggested for WavPack, up to -b4.55x5s.5, and I still hear that hiss. Aggrrrhh! Since this sample sounds more like regular music than a proof of concept, I have a panic at the thought that other music could be compressed in such a low-quality way. So I suspend the use of the hybrid WavPack and hope that @bryant will be able to fix it.
Look at my ABX tests in this thread. I've managed to ABX Wavpack up to -b576x4s0.5
If you want peace of mind with wavpack lossy, 450k range is not enough for this sample.
As @shadowking said, this sample raises suspicion on how it is recorded/mastered so it could be artificialy created.
No one knows... I would say that this sample is good to "calibrate" other lossy encoders and listen how they work on this sample but
it shouldn't be of any concern in real life music IMO.
If you want really strong setting (and peace of mind) for wavpack lossy for this sample you need something like -b550hx4s0.5.
Anything lower is ABX-able (at least for me). for faster encoding you could try -b576hhs0.8 but this high bitrate defeats purpose of economical encoding to save space.
It's up to you which way you want to go.