I use an airport extreme to connect both BeoPlayer and BeoConnect to my BM5. The BM5 is connected via ethernet to the airport. The computers talk wirelessly. When I have big transfers, I connect the computer directly into the airport. This has all been working fine for about a year.
For BeoPort, you would just connect this via MasterLink. There is no need for ethernet (in fact, the BeoPort doesn't have ethernet so I'm confused about this question). However, I don't know how a BeoPort will operate in a system with a BM5. I removed my BeoPort when I added the BM5 and replaced it with a BL Active.
Step 0: Have you registered with Bang-Olufsen? Click on "registration" on the BeoConnect screen and follow the directions - I don't know if this would stop you from connecting, but it will stop you from seeing all of the N.Radio stations.
Step 1: Go into the "expanded menu" on the BS5 and verify that the BM5 can see the network (set the wheel to "Settings", then press >>, <<, >>, <<, GO), then look under Network Info and Internet Connection should be "YES". If the BM5 doesn't see a network, then figure out why. If it does see the network, note the hostname (should be BEOMASTER5) and IP address (should be similar to the ip address of your computer except for the last number, for example, my computer is 10.0.1.2 and my beomaster5 is 10.0.1.10).
Step 2: Can the computer "ping" the BM5? Open a terminal prompt on your mac and type "ping beomaster5". If this does not work, then see if you can ping by IP address (that you noted when looking at Network Info under the "expanded menu" of the BS5 - e.g. ping 10.0.1.10). If you can ping via IP address, but not by "beomaster5", then enter the ip address in beoconnect and see what happens.
Step 3: If this doesn't work, then verify that both your computer and the beomaster5 are known to the airport: Open the "Airport Utility" and select your airport, then select "manual setup" -> Advanced -> Log and Statistics -> DHCP clients. Look for your computer's IP address and/or name and the beomaster's IP address and/or name. Since the BM5 is hardwired to the Airport, it should be there. If not, then chances are your ethernet cable is bad (make sure the little lights next to the ethernet connection on both BM5 and airport are blinking).
You might also try hardwiring you computer to the airport just as a test (to eliminate any issues that might be coming from wireless - although if you can surf the internet wirelessly from your computer than you should be able to connect to BM5.
One other thought - make sure you're not using the "guest network" feature of the airport - if you're connected to a "guest network", you cannot connect to local computers on the network, only the internet. You can find this setting in the airport utility under "guest network".
The password is case sensitive meaning you need to enter everything in UPPER CASE (I don't think the BS5 let's you enter lower case letters on the password screen).
Hopefully this will help you diagnose your issue.
Stan