ipxe and imacs with Broadcom NetXtreme BCM57765 cards

[robinsmidsrod]

If I'm not mistaken, the iMac uses the Broadcom bnx2-based card that is not well supported. You might have luck if you try the work-in-progress rewrite of the bnx2 driver from this year's gsoc project: http://ipxe.org/gsoc/bnx2/

This means you'll have to check out that specific branch, compile it and build the ipxe.iso as explained on the normal download page. As this is work-in-progress, it is highly likely that it will not work. If this seems too tricky for you, you have no other option than to wait for this driver to be reviewed and merged into the main release, or sponsor development of it to speed things up.