It stands to reason that the GXW and analog lines are remote from the PBX and are at the site of interest. The GXW does not have the native capability to route based upon dialed number, so the task falls to the PBX to route the call. You can place another GXW4104 on the site and connect the analog lines to it and then setup as a SIP trunk to the PBX and route the 911 calls from the 42XX to the PBX and then to the 41XX for local 911 calling.
You may also wish to consider using some HT503 or 813 ATAs (have not used a 813 yet) as these have both an FXO and a FXS port. You can then connect to the PBX, but at the same time connect a analog phone to each so that you can take advantage of the life-line function.