AMIS RC2 and TTS plus Audio

I love the most recent versions of AMIS that now support the use of text only DTB3 allowing the use of my own SAPI voices but have run into something odd that I think should be considered as a new feature. When I load a self-voicing DTB3 such as one created with the DAISY Translater (Save as DAISY, full option with audio), and then load that version into AMIS, I have not been able to switch from the prepared audio to the use of my own TTS engine. This would allow the player to act as thought the loaded DTB3 was text only. Have I missed a preference setting or is this simply not an option? I suspect that it was not considered necessary but with some some audio files, the reading rate can be set much higher using TTS. At times, it may be better to listen to a human voice recording and at other, to move more rapidly than is understandable when the pre-recorded human voice is set to a higher reading rate. Thanks in advance for any thought you might provide about this. As the head of the NIMAS Technical Assistance Center in the US, I am very interested in supporting DIASY and in providing options for students with print disabilities.