Disklavier

I have purchased an Apple Express and need to figure out how to set it up as a "Client" to 
allow the Mark IV to connect with the internet using a Airport Base Station hooked to a 
Macintosh running internet.

I thought this would be easy, but have run into problems as well as confusion.  I have read 
over the threads in the forum discussing "routers", etc. for accomplishing this.  I  have run 
into  a problem according to the info I have read online about this device, it does allow the 
device to become a "client" to "access point on the Mac airport base station.  But it seems 
that when the Apple Expess is in the "Client mode the ethernet cable does NOT work.   

Am wondering what to do.  Seems that I recall mentioning setting this Apple Express up 
first as a client without connecting the disklavier and then once this is done, then connect  
ethernet to Mark IV and the Apple Express.  Does this have a chance  of working?

Has anyone tried to connect their Mac's with a device similar to this and if so how?  

Thanks for the help in advance.  I have already subscribed to the Disklavier Radio and am 
presently directly connected via ethernet cable to a portable Mac, but would like to free 
the portable up for other things. 

Joan