[Koha] How to catalogue related items?

[Mirko]

I have a "sorry-i'm-not-a-librarian"-question:

How do I catalogue several items that belong together? For example:
I have a series for language learning: one workbook, one grammar and
two audio cds. They are not a single kit containing all items but
have seperate call numbers and can be used/checked out independently
of each other. Nonetheless they are related and this information
needs to be available to the patron.

I thought I would set up a biblio containing the general information
(title, author etc.) and have items for workbook, grammar, cds with
their respective call number/barcode.

Somehow this seems to be the wrong way to do it:

- I can only have one item type (for the biblio, not for the item)
-- but i want patrons to be able to find for example the cds if they
search for audio materials -- so this seems wrong

- I used "Materials specified (bound volume or other part)" to put
"CD 1", "CD 2", "Workbook"… but that information only shows up in
the staff client. When searching the OPAC I don't get this info,
neither can I do anything with the items of the biblio (like, place
a hold), I can only look up "Item type", "Call number" and "Status".
There is also a field "Location", but it is empty (it is filled in
the staff client).

What is the correct way to catalogue several different items that
somehow belong together? If I have to make a seperate biblio for
each item, how do I connect them? Patrons should be able to see that
(for example) there are also audio cds when they see the record for
the books (etc.).

I hope it is clear what I'm trying to do, any help is appreciated.