Dave Smith Instruments SYNTHESIZERS

Hi everyone,
I have an evolver and a Tet4a. I have a PCR-800 controller to use with them. Evolvers only have midi connections but both the PCR and Tet4a have midi and USB. I also have a UM880 midi interface. I want to be able to use the Mac (osX 10.6) to use the editors with them and also use the PCR-800 to control them. I am not sure how to best connect it all up. I can see the Tet4a, PCR-800, and the UM880 in the audio midi setup utility but cannot make interconnections between them. I have both midi connected to the um880 and usb connected to the mac.
Anybody got any helpful hints?
thanks