Using this toolbox you can open up additional cubes and draw iso-surfaces from them in the rendered scene (this works for both the iso-surface and volume rendering toolboxes). This allows you to compare data from different energies and sources.
Choosing the data and selecting levels should be straight-forward (note that the Go menus provide a simple way to select a cube you've previously opened). A cube can be temporarily removed by de-selecting the Display: checkbox. Note that to display the iso-surfaces, or see any changes, you must press the Draw button in the rendering window.
By default GAIA will use any coordinate system information to align the iso-surfaces of the extra cubes to that of the displayed cube. So you should see a scene in which the cubes are aligned correctly on the sky and along the spectral axis.
Sometimes you'll want to align cube using their simple grid positions. To do this you need to de-select the Match coordinates item in the Options menu.
The other coordinate matching options are Match sidebands and Match using base system.
If you select Match sidebands and you have heterodyne cubes with suitably defined dual-sideband spectral coordinates then this will be taken into account when matching (otherwise matching will just use the frequencies or velocites of the current sideband).
Match using base system: when matching spectral coordinates it is usual to achieve this by transforming all coordinate systems into a common system, this system is wavelength by default. For some systems it may be better to use another common system so by selecting this option (which is on by default) you can set the common system used to be that of the current spectral axes of the main cube. This option is most useful when working with velocities, when you want the alignment to happen in that system (because the spectra have different rest frequencies).