Basic Question about Networking

In theory it should work. Why don't you just try it. Connect Ethernet and try accessing W-Lan. I know atleast on windows it is possible to connect to two different Ethernet LAN networks at the same time. There is no reason why it shouldn't work.
I don't know what happens if you have two Gateways set. I would avoid it but with your setup there is no gateway for Ethernet anyway.

 

Wrong question. Connect your modem to a wireless router with LAN ports. Connect your iMac wirelessly to the router. Connect the Blu-ray player to the router via Ethernet.

However, I am not aware of a Blu-ray player that acts as a media server. It may access content and download firmware updates from the Internet. Most of the Internet content that you access via your Blu-ray player can be accessed directly through your computer.

Blu-ray players transmit content to TV sets, preferably via a HDMI cable. They do not transmit content via Ethernet.

 

Your advise is correct however I think he wants his BD player to access media from his iMac (DLNA I assume).

 

I'm still a little hazy on exactly what you need, but it sounds like getting a second router to act as a wireless bridge might do what you need.

If the problem is that your modem and router are too far from your Blu-Ray player to let you easily run a cable between them, just get the second router, set it up to extend your original wireless network, then put it right beside your Blu-Ray player.