We also use cdosys for our e-mail. Actually, most of my clients are fully upgraded to 2005 but our software still uses the cdosys stored proc that was written...

for database comparison, I use sql effects clarity ce which is the free version.

edit_11/9/2009: FYI: the name has been changed to SQL Accord CE

Have you tried selecting the formula instead of a summation?

ie: select '=A1-B1'