Having trouble configuring a second BM server to enable webaccess connections

First BM server is configured with static NAT and access to GW Webaccess is
working fine.

Attempts to configure the second BM server in the same fashion failed.
I believe due to default routes on our LAN switches directing replies via
the first BM server.
Attempting to configure reverse proxy as an alternative has been equally
soul destroying. Even with filters disabled I am only rewarded with an
Error 503 on the browser of a pc set-up outside the firewall, a hint that
something is getting through to the GW server but being ignored.

Border Manager servers running NBM3.8sp4ir2a plus the Craig Johnson
proxy.cfg and tuneup files. GW system is a single machine, GW6.5SP4.

I would appreciate any advice on how to progress as this is becoming a
little less than fun.