Welcome Dubpete,
There is not an easy fix for this... Winamp doesn't notify plug-ins in time that a new song is starting (in fact, it sends the event about one second later). So there's no way of knowing when cross-fading would be needed.
Depending on what you want and how difficult you want to make it, there is a solution though: Use Winamp without Stereo Tool, use the stand alone Stereo Tool version to process the output. But if you do that, you need to find a way of feeding the Winamp output into Stereo Tool.
If your sound card supports it, you might be able to forward audio output from one program into another (for example some ESI sound cards have this option). If not, you can use a program Virtual Audio Cable (costs $20) to do this. Or, if you have multiple sound cards, you can capture the output of one and use the other for the Stereo Tool output.
Alternatively, you could replace Winamp by a radio automation program such as SAM4 or RadioBOSS - but they are quite expensive. The advantage of this is that these programs do the cross-fading before feeding the result into any plugins. And you can easily add jingles and sound effects
Note: There might be other programs (other Winamp DSP plugin compatible players) that do the cross fading themselves, if you find any please let me know...