David's blog has a lot of useful information in the comments section, but I am writing this comprehensive guide to save you the trouble from searching through the all the comments.
I will describe Tim's method on this post since I think it is easier to use after you have successfully setting it up.
However, Tim's method requires a bit of Terminal knowledge. If you don't know what Terminal is, don't worry. This post will have a step-by-step guide to help you to enjoy A2DP on your Mac.
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*I suggest you download the following 2 items onto your Desktop
1) Download a2dpcastAudioDevice.tgz file from http://www.coolatoola.com/a2dpcastAudioDevice.tgz
2) Download a2dpcast from http://www.coolatoola.com/a2dpcast-0.3.zip
3) Turn on your built-in bluetooth on Mac OS and allow your bluetooth stereo headset to pair with it. The usual default passkey for bluetooth equipment is 0000 (as in four zeroes).
4) After pairing, go to Preference->Bluetooth->Devices. Click on the name of your device and copy down the Device Address. It will be in aa-bb-cc-dd-ee-ff format (12 characters).
5) Launch Terminal. What is Terminal? It is similar to the "command prompt" in Windows or the "Terminal" in Linux. You can access Terminal by:
Click on your Mac HD -> Applications -> Utilities -> Terminal
6) A new window will pop up with the word "Welcome to Darwin!".
Type the following and press enter:
cd /
7) Type the following and press enter:
sudo tar xfzp DOWNLOAD_DIR/a2dpcastAudioDevice.tgz --same-owner
where DOWNLOAD_DIR is the directory where you have downloaded/saved the file
For example, my Mac OS user account name is linkopia and I have saved my files on desktop. So I will type the following:
sudo tar xfzp users/linkopia/Desktop/a2dpcastAudioDevice.tgz --same-owner
Terminal will ask for your password. Type in your password and press enter.
8) Type the following and press enter:
sudo kextload /System/Library/Extensions/AudioReflectorDriver.kext
9) Double click on the a2dpcast-0.3.zip to extract the zip file. A new folder called a2dpcast-0.3 will appear.
10) Click Finder. You will then see "Finder", "File", "Edit", "View", "Go" ... on the menubar on top of your screen.
11) Click "Go" and choose "Go to Folder".
Type in the following:
/usr/local/bin
and click Go
12) Copy the file "a2dpcast" from the a2dpcast-0.3 folder to bin folder. Mac OS might prompt for login name and password or confirmation to copy the file. Allow the file to be copied to bin folder.
13) You are almost there. Now go to Terminal again. Type in the following and press enter:
/usr/local/bin/a2dpcast aa-bb-cc-dd-ee-ff
where aa-bb-cc-dd-ee-ff is the Device Address of your Stereo Bluetooth Headset.
**If your music skips, you can try to lower the sound quality. I think the default value is 32 (You can change the value anything from 0 to 32, the lower the value, the sound quality gets worse). So you can type the following:
/usr/local/bin/a2dpcast aa-bb-cc-dd-ee-ff 20
14) Launch iTunes and enjoy your music wirelessly!
15) Leave the Terminal open while you are using A2DP. You can minimize it, but don't close it! Go to Terminal and press "Enter" to stop A2DP when you don't want the stereo bluetooth anymore. You can close the Terminal now.
***When you want to use A2DP again, enable your Bluetooth on Mac OS. Launch terminal, and type the following again:
/usr/local/bin/a2dpcast aa-bb-cc-dd-ee-ff
or
/usr/local/bin/a2dpcast aa-bb-cc-dd-ee-ff 20
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Enjoy A2DP on your Mac OS 10.4 (Tiger)!
If you encountered errors while going through the steps above, click here to read about some workarounds that might help you to get a2dp fully running.
A2DP (Stereo bluetooth) on Mac OS Tiger (10.4) - (2b)
This worked quite well on a G4 PPC 10.4 Tiger 1.2 GHz with 1 GB RAM, on a similar G4 with only 400 MHz processor sound was choppy.
Bluetooth stuff is IOGear dongle and Insignia Headphones from BestBuy/Futureslop.