Problem solved - in this instance what we needed to do (and not documented ANYWHERE) is to save the configuration prior to attempting to test that configuration. Without doing so, the message one gets is that the card is not responding at that base address setting.
The detail I've provided is minimal, and serves only to act as a reminder should we encounter the problem somewhere down the line...if anyone out there wants more elaborate detail, I'd be happy to provide it...I have email notification set on if someone replies to this message, so I will see the request.
