You only need to find kde in the repositories and install it. You can
either install just the desktop or the entire kubuntu software set depending
on your requirements. From what you described, I would think you only need
the kde desktop.

The newest Ubie you can install the the Studio stuff with out installing the
realtime kernel. I got my stuff working.

But isn't what you describe the reverse of what I intend to do?

You have likely found the kernel used with Ubuntu Studio is compiled
differently than that used with Ubuntu or Kubuntu. One of my machines
runs Ubuntu Studio but the use is very limited for me. It is no problem
to set-up a machine that is running Ubuntu for the KDE desktop but with
Studio many conflicts exist with programs.

I would suggest downloading a copy of Kubuntu and installing it on a
different partition. Have you noticed that Studio has limited options
for word processors and many of the programs that are pre-installed on
the other Ubuntu distros? I believe that the kernel is called a
premptive kernel, but that is a guess as I researched it a few years ago
and my memory is questionable. Anyhow you don't want to mess with the
kernel because the time slices are much different than is in the other
distros.

No, I hadn't been aware of differences in compilation. (I know what
compiling is, I know that Linux may require compiling downloads, but
there my knowledge currently ends.)
I assume that that has to do with the time slices you mention.

The idea of a different partition appeals to me, although I can't
clearly see the consequences. But in a fews days a friend will visit
me who is experienced in Ubuntu (and other distros).

I hadn't yet noticed the limited options for word processors.
Moreover, I have the free previous version of a multiverse Office
suite installed. (The suite that I also have on my Windows and Windows
Mobile systems.)