Kolab from individual components

[Promani NV]

Hello,

I'm researching the possibility to use Kolab to replace
an Exchange server (OK that's what everyone probably wants).
On the client side I've tried Bynari with a regular IMAP
server. I would also like to use Horde.

However, I do have most of Kolab's components already running
on another server and spend a lot of time configuring. It would
be a shame to throw away all the tweaking work, so I'd like to
know what 'added value' Kolab provides over the individual 
components and has anyone "cloned" Kolab on their own? Is
this a doable thing (eg are LDAP schemes available and how
would the free/busy be handled, etc).

Regards,
Joris