I believe that the column that gets displayed after you select it, is the bound column only. What I've done if I want to show more than one column, is to create a new "field" with SQL of what I want to show and use that as the bound column. It works great for me. Make sense?
SELECT Field1, Field2,
Field1 + ' | ' + Field2 AS CmbField
FROM dbo.Tblblah
With this example, I'd use column 3 as the bound column.
-Heather