I've also tried other clock settings, all have exactly the same symptoms.
I can see the TXEN line going high any time a packet is sent, like DHCP requests, but I get nothing on the other side.
I've modified the example ethernet test program to customize bootstrapping options to minimize external part count by manually resetting/un-resetting the ethernet.

Any recommendations would be welcome! I've been stuck on this for about 20 hours.