The question is not to find a way around it, the question is why it behaves that way in your Project.
A Producer Kit is just a Summing Stack, were all the individual Channel Strips (Subtracks) are routed to the same Bus that the Master Stack Channel Strip uses as its input.
In the example of the screenshot, the Summing Stack uses Bus 2, but I selected different Outputs for the firstsix Subtracks, even a Surround Output, whatever is available under the Output Selection Button. Only the "Tom High" Channel Strip is still routed via Bus 2 to the Master Stack Channel Strip.
You can find more in-depth explanations about the Drummer in my graphically enhanced manual "Logic Pro X - How it Works".
Try to use a different Project and see if you can change the output routing there.
Hope that helps
Edgar Rothermich
http://DingDingMusic.com/Manuals/
'I may receive some form of compensation, financial or otherwise, from my recommendation or link.'