The diagnostics software supplied with the Conexant 3805 based cards is thoroughly well designed and feature rich. There is a vast amount of information available to the user although the majority of people will never need to know or be concerned about what is happening behind the scenes.
The "Protocol Setup" pane is where those dreaded VPI, VCI and Encapsulation Mode settings reside. When I installed the modem, all of these values were automatically set correctly. Ensure that your settings match the ones pictured below.
The software provides information about line quality including downstream attenuation (known as the WOOSH test).