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You can never find one of these when you need it this one's a compression wave simulation

Thanks so much for sharing that video. It + your explanation clears things up enormously for me!

I can understand why there aren't many tutorials about this - although it is a very simple principal, it is quite hard to put into words what is going on. Here is one about rails in general, which of course are not specific to spline wraps. However they all work in a similar way. A rail works by being offset from the original - the distance doesn't matter. What does matter is the direction of offset of each point in the rail from its equivalent in the source. This is very easy to understand and predict when the splines only curve in one direction, and when that is the case it is quick and simple to find the right offset angle by experimentation alone. However, when you're dealing with elaborate knotwork like this, then curves are going on true 3D space with tangents not on world / planar vectors, so in those circumstances it becomes very tricky to know what the offset directions should be. But that is why getting a rail from create outline is sometimes a good idea, that way the tangents match all the way along the spline. But if that doesn't work, then the only way is to go along the rail point by point, rotating it around the source until you get it to do what you need it to do... CBR

You have the render region enabled. by default it runs at half res to speed it up. You see that tiny white triangle on the right hand side? drag it up to the very top for full resolution

Here's the navigation for hierarchy up_down_iteration.c4d this file just does one plane - you'll probably have something like this for all planes

Well, your settings look right, and having just checked that metaballs do render in the PV using the native renderers (they do) I can only assume this must be a problem with Metaballs and Octane, possibly related to their parametric nature ? I presume your particle settings numbers are also identical in both VP and render ? You could try putting the MB inside a connect object, or remesher (also seriously improves the topology) or making it editable (if that is an option animation-wise). Might be worth uploading the scene file to see if we can replicate. CBR