Hi ... I have a Digital 192 hooked up to a AD-16x and a DA-16x ... that works perfectly fine ... Apogee sells a special cable that splits the AES i/o to each unit.
On the standard 192 however, they come with 8i/o analog, and 8i/o digital. So, If you want to hook up a DA-16x to that and get 16AES out, you need to buy the digital expansion card for the 192. As I am sure you know, a 192 can only send 16 i/o at a time. You can make a combination of analog and digital per interface, but only a total of 16i/o. So by running 16out to the DA-16x, you won't be able to run any analog outs.
So, to run 2 DA-16x's, you would need 2 Digital 192's to get a total of 32 outs(AES).
As for clocking? I have no idea. I know that apogee has a PDF for hooking up the Big Ben in a Protools environment.
http://www.apogeedigital.com/pdf/con...protoolshd.pdf
I hope that helps a bit
Ian
p.s. I am assuming that you are hooking the DA-16x's throught the digital i/o of the Digi 192 ... if you are using the Apogee X-cards, then forget what I just said.