I will do the zlib update as you have suggested to hopefully resolve the initial error.
As far as the remaining 'The PHP binary coming with ISPConfig does not work properly on your system!' error is concerned, I have followed the other post and found that I did not have 'mysqlclient10-devel' and 'mysql-bench' installed. Perhaps these are causing the issues?
I will make the adjustments, re-run the setup and let you know.
Thanks for your help Till.