The diode is for protection.
The filter is a first order low pass filter:
![](http://guitar-fx-layouts.238.s1.nabble.com/file/n47757/400px-RC_Divider.png)
So you need to add large electros to ground from the top row. 100u is pretty standard.
I don't think jfets are more appropriate than op-amps for buffers or splitters, but jfet splitters work fine too, with slightly lower output than the op-amp version. There is no power filtering or protection on that linked vero either, so you could add it the same way.