Well, I have done it, - finally! :) I have upgraded successfully a 24" iMac 7,1 and a 24" iMac 9,1 with an original 802.11ac & BT 4.0 Apple Broadcom BCM94360CSAX combo card. So far I can say the WiFi and Bluetooth functionality is working perfectly (and independently from each other) under Mac OS X and Windows 7 & 10. The original two 802.11n and the Bluetooth antennas can be reused (with adapters), - although they are of course not 802.11ac optimized.
Okay, what's needed?
- an Apple Broadcom BCM94360CSAX combo card, approx $10.- on ebay
- an Apple Broadcom BCM943602CS (BT 4.1) combo card, approx $17.- on ebay
- a compatible M.2 (NGFF) to mini PCIe adapter (also named as BCM94360CD to mini PCIe adapter), approx $4.- on ebay
- 3x U.FL female to MHF4 male plug antenna adapter cable, approx $3.- per piece, so total $9.- on ebay
- a 10mm to 12mm washer (to hold the M.2 to mini PCIe adapter at its position)
- a small piece of electrical tape (for isolating one side of the washer)
Note, - the washer is not needed if you buy a (compatible) adapter with two "mounting jut" (left and right). My adapter had only one "mounting jut", - at the wrong side.
However, - regarding the hardware cost this will give a total of around $30 per 802.11ac & BT4.x upgrade.
Why I have chosen the BCM94360CSAX card? Simply answer, because it has only 3 antenna connectors! The BCM94360CD would also work but it has 4 antenna connectors. So on an iMac, there would be one antenna too little. (Installing a fourth antenna can be a very hard task.) Regarding the antennas it was unclear for me in which order these should be connected to the new BCM94360CSAX card. On the installed card I decided me for:
white cable (topmost connector) J0 blue cable (middle connector) J1 black cable (lowermost connector) J2
Update: 20.12.2016: My first antenna config seems according the several Apple 802.11ac upgrade threads not "right". The J2 connector should be always used for Bluetooth. This will result in the following alternative configuration. (I have tested this meanwhile and I can confirm that this config may work somewhat better.)
- white or gray cable (topmost connector) J0
- black cable (middle connector) J1
- blue cable (lowermost connector) J2
Maybe someone finds a further (better) antenna configuration. If so, - please report here. ;)
This relatively simple 802.11ac & BT 4.x upgrade will work for any 2007, 2008 & (early) 2009 Aluminum iMac computer.
All more recent Unibody Aluminum iMacs (late 2009 and above) needs unfortunately, like some Apple Mac Pro models, a special ("version 3" labeled) mini PCIe adapter with external USB cable. This makes the whole upgrade process MUCH more complicated. To "strip down" the mini PCIe slot design at these newer iMac models is a totally stupid & myopic decision. Really weak Apple! :(
So much for that... Nice to know, - the minimum Mac OS X version will be different. Because of the needed 802.11ac drivers the lowest supported OS will be 10.8 Mountain Lion, recommended is Mac OS Mavericks 10.9 and later.
IMPORTANT note, - there (may) exist furthermore also a software issue on the 2010 and 2011 iMac model range. The 802.11ac upgrade will also work, but you will run into problems with the OS X Internet Recovery feature. As a result you will have at every startup a strange error message. It seems that the OS X Internet Recovery which is incorporated into the EFI firmware is not able to recognize a 802.11ac card. As a workaround you can make a firmware downgrade below iMac EFI Update 1.8 which will remove the whole OS X Internet Recovery feature. The following models are most likely affected by that annoying problem: https://support.apple.com/en-us/HT202313
Some last words to the (2015) BCM943602CS combo card. Main difference to the BCM94360CSAX combo card is support for Bluetooth 4.1. The BCM943602CS card will NOT work under OS X Mavericks 10.9, - it needs OS X Yosemite 10.10 or later. There exist also no official Windows 7 support from Apple for that combo card. The available Windows 10 drivers seems to have currently some stability issues (as of December 2016).
For more information regarding the installation check my pictures, - sorry for the bad photo quality. ;)