Changing the code on an external link.

I am using a program that gets data from a quote service.

=PROPHETX|QUOTE!'CN6[DTN:CBOT]?Settle'

This code will get the settlement price for CN6. What I want to do it change this code to have the CN6 be cell location C8 on my page. I have tried several things but the system thinks im looking for the settlement price for C8 not what is located in location C8 on my spreadsheet. Anyway you get the picture. Any ideas?

=PROPHETX|QUOTE!' & C8 &[DTN:CBOT]?Settle'

This is not work either.