Expanding I/O capability on the UA-25ex using the digital I/Os.

Is it possible to add more inputs and outputs to the UA-25ex with an external preamp that also has the same toslink s/pdif I/O's?
 
 I want to be able to hook up hardware effects and send tracks out to them and then route them back into Sonar on another input. Or record more than 2 mics at once onto seperate tracks.
 
The UA-25ex has a pair s/pdif I/O's. I read somewhere that these are 2 channel. Does that mean that mean I can only send and recieve a single stereo track or two mono tracks using the digital I/O?  Or can it send and recieve more? Can I hook up an 8 channel mic preamp with digital output and route each channel to a seperate track in Sonar?
 
Or should I just buy a new interface with more I/Os?