Streaming GDSII files

I stream my chip layout to GDSII file. The thing is the process I use is modular and there are modules which I do not use, but the layers associated with those modules are still being streamed to gds file.

The foundry highlights an error saying "you have these layers, but they are empty". So I contacted their helpline and they simply say "if you do not use a layer, just do not stream it".

But this is easier said than done. The process is a 6 metal process, but I use only 4 metals (the foundry allows for it). So I should disable the streaming of the two remaining metal layers. Where do I do that? I set only three options in stream configuration window: gds file name, technology file, and technology layer map file. Everything else I leave as is. I do not find an option to manually select which layers I want to stream. Do I have to delete the corresponding lines from the " *.layermap " file to exclude these layers from the stream or is there another place  for doing that?

Another thing, it is fairly easy to figure out which layers are associated with metal 5 and 6. But  there are technology layers related to "multivoltage wells, islands, implants, diffusions" etc. that I do not use and they are a mystery to me. How do I know which layers can be safely excluded from the stream?

My Cadence environment is cleverly configured (using foundry install script) and layers I do not use in the design do not appear in Cadence environment, i.e. metal 5 and 6 are not present in layer palette in Virtuoso Layout, however met 5 and 6 are still present in generated GDSII file. Those metal layers are empty and foundry is highlighting this fact as an error. And the foundry helpline says "do not stream them".

So, where do I configure the layers I want to stream and how to identify the layers I can safely exclude from the stream?

And, Is there a tool (maybe not from Cadence) that would show information about the GDSII file like number of layers, layer names, cell names, etc ? I know I can import the gds back to Virtuoso but I want to get some statistical info about what is in the gds rather than a viewer of gds art.