I am attempting to build an application using the ArcGIS JavaScript API that will allow my users to research competitor pipelines across the country. The main layer in this application is comprised of a large feature class containing over 673K features. One major aspect that I want to give my users is the ability to "filter" features. For example, show only pipelines of companies X, Y, & Z that are transmission, and greater than 24" in diameter.
Another major aspect is that it has to be simple to use. I have been experimenting with using ComboBoxes so that the possible options are already populated in the list. By using more than one of these for each field I can create a simple way to create a SQL query of sorts. The problem I have with the ComboBox is that only one option can be chosen at a time. But with nearly 2000 possible options I'm not really sure what else to use.
Any one have any ideas? Is there something that I am overlooking? Has anyone spent much time using the EnhancedGrid?
I have added the image below that is using an EnhancedGrid. Could it be possible to use the "Check Boxes" as a selection method.

Thanks for you input.
-Mike