Avaya IP Office SIP Trunk Issue

would like to get your take on a resolution to my SIP trunking dilemma.  i am configuring a SIP trunk  to a provider with the network architecture as:

PBX LAN 1 -> firewall -> provider network

we are successfully registered and inbound and outbound calling is working.  however, audio inbound to the IP office is not working.  so in other words, when you call into the IPO you can hear the person but they cannot hear you.  after much packet analysis on the provider side and on the IP office side it seems that we have narrowed the issue down to SDP.  the provider is seeing SDP information to send audio back to the IP address assigned to LAN 1 (192,168,168.30) of the IPO which is behind the firewall.  i need the IPO to send SDP information to let the provider know to send audio back to the IP address of the firewall outside interface (10.179.8.2) so it can then be port forwarded (PAT) back to the LAN 1 IP on the IPO.

192.168.168.30 = IP Office LAN 1 (LAN 2 not in use)
10.179.8.2 = firewall outside interface
10.128.2.40 = provider switch (ITSP domain name)

below is a packet capture on an outbound call that completed showing the SDP info on the IP office side and in red are the IP address parameters that need to be changed to the outside interface of the firewall (10.179.8.2).  is this possible?  i have never had an issue with this before and have confirmed other SIP trunks i have setup are not affected by the private IP of the IPO LAN 1 showing in the SDP info and all other factors being equal:


any and all help is greatly appreciated.

[color #204A87]4244276mS SIP Tx: UDP 192.168.168.30:5060 -> 10.128.2.40:5060
                    INVITE sip:xxxxxxx@10.128.2.40 SIP/2.0
                    Via: SIP/2.0/UDP 192.168.168.30:5060;rport;branch=z9hG4bK63bea030317fe3f9cac9ab31d48a8fee
                    From: "Anonymous" <sip:xxxxxxxxxx@10.128.2.40>;tag=66db1c96bc5af4d6
                    To: <sip:xxxxxxx@10.128.2.40>
                    Call-ID: 375a90c5a765f49b42085cd41f8ac677
                    CSeq: 1609181771 INVITE
                    Contact: "Anonymous" <sip:xxxxxxxxxx@192.168.168.30:5060;transport=udp>
                    Authorization: Digest username="xxxxxxxxxx",realm="10.128.2.40",nonce="a89141600011",response="55115662b590b77777ca56b79e8ae97a",uri="sip:xxxxxxx@10.128.2.40",algorithm=MD5,qop=auth,nc=00000007,cnonce="086d331e52366b1f4ca8"
                    Max-Forwards: 70
                    Allow: INVITE,ACK,CANCEL,OPTIONS,BYE,INFO,NOTIFY,UPDATE
                    Supported: timer
                    User-Agent: IP Office 9.1.0.0 build 437
                    Content-Type: application/sdp
                    Content-Length: 301
                   
                    v=0
                    o=UserA 3773082749 329259799 IN IP4 192.168.168.30
                    s=Session SDP
                    c=IN IP4 192.168.168.30
                    t=0 0
                    m=audio 8000 RTP/AVP 0 8 18 4 101
                    a=rtpmap:0 PCMU/8000
                    a=rtpmap:8 PCMA/8000
                    a=rtpmap:18 G729/8000
                    a=fmtp:18 annexb=no
                    a=rtpmap:4 G723/8000
                    a=rtpmap:101 telephone-event/8000
                    a=fmtp:101 0-15[/color]