Hi guys, thank you very much for your help and attention. The technical support on this forum is top notch 
I am using the ADSP21469 Evaluation board, so lease confirm if my understanding is correct:
According to the schematic, the "CLATCH" pin of the AD1939 is connected to the Device Select of the Sharc (DDPI_P4 pin) via a slide switch (SW3.4). The Slave Select from the USBi connects to this node as well, assuming you connect it using the method described in Section D of the User's Guide. It seems the same latch from the USBi controls both the AD1939 and DSP.
The software seems to verify this case. When looking at the hardware tab in Sigma Studio, both the DSP and the AD1939 are connected to ports labeled "SPI 0X1 ADR0" on the USBi module. If I change the address on either of these ports, I get no response from the corresponding device.
After trying Dave's suggestion, the only address I can read data from the AD193x module is from "SPI 0X1 ADR0". Any other address shows everything muted and powered down in the AD193x window.
This is where I am left:
It does seem that I am able to communicate with the AD193x to some degree, but it still changes a lot of my parameters automatically on me.
Should I try using separate latches from the USBi for the DSP and the AD1939, so each will have their own individual latch? I understand I will have to wire this up manually.
Thank you for all your help.
- Justin