how can I merge multiple FrameMaker TOCs/IXs into one RH TOC/IX
I am trying to link a single RoboHelp project to mulitple FrameMaker books. So far so good---from the WebHelp layout, RH generates the files and I can view each book in my browser---but I cannot find a way to merge the individual Frame TOCs and IXs.
I have a User's Guide, an Installation and Adminstration Guide, and a Plugins Guide in Frame. Each is a separate book, each has its own TOC and IX.
In RoboHelp, I have a redseal_docs project which I have linked to each of the three books. In the Project Manager, I right click on the User's Guide and open the Properties dialog, where I enable conversion of TOC and IX, creating new RH TOC and IXs named usr_gde.
I generate the book, it looks good, Frame TOC and IX are correct.
Then I right click on one of the other books and enable conversion of TOC and IX, but my only option is to create a new RH TOC and IX. The Add to existing... options in the dialog remain greyed out and not selectable.

The end result is that I can have TOC and IX in RH from only one of the three Frame books, when I want one RH TOC and IX to consists of a merge of the three.
Is that reasonable? Can RH do it? And if so, how?
Thanks.
