Yes as RTIInstaller has stated, you NEED a 'TDM Ribbon Cable' in order to connect additional cards to your system... It allows the additional cards to share data along the TDM bus.
The Ribbon Cables come in varying sizes with different numbers of connectors (referred to as 'Nodes')... the most common being the '5 Node' size. A '5 Node' cable can be used with only a 'Core' and 'Farm' by just leaving the last 3 nodes unconnected... be aware however that Ribbon Cable AND Cards both have polarity markings (triangles) that must be observed.
The other cable you need is the 'Interface Cable' which will connect your 888's 50 pin connector to the 'Audio Interface Port' on your Core/Farm card.
If you happen to be interested in making your own cable, here is some info.
http://macos9lives.com/smforum/index.php?topic=786.0All of the software to get you going is here on the OS9Lives site.