ISA Server 2006 Publishing Rule

Hello,

I have an External ISA Server 2006 SP1 with:

WAN: 192.168.1.250 (talking to the home ADSL Router)

DMZ: 192.168.2.1

I have an internal ISA Server 2006 SP1 with:

DMZ: 192.168.2.3

LAN: 192.168.8.1

In the DMZ I have placed a Edge Transport Role, with a NIC: 192.168.2.2

So, I am trying to publish the OWA in the External ISA Server, but I don't know whether the external ISA Server should point to the Edge Transport Server or to the internal ISA Server in that Publishing OWA Rule.

The SAN Certificate (Autodiscover.domain.com, mail.domain.com) has been placed in the CAS Server, both ISA Servers and even in the Edge Transport Server, and the Root Domain certificate also has been place on those servers, because none are domain-joined.

Thanks in advance.

P.S: Maybe this is more of a Exchange related question?