If you have read the Tim Hewett's method to implement A2DP on your Mac OS 10.4 (Tiger) - (2a) and have problems with the sudo kext command, this post will try to assist you to get things going.

Again, the errors and solutions stated below are obtained from the the user comments at David Connolly's blog. This post is to summarize the most common problems mentioned and how to solve them. (and save you from going through 200 comments)

Common errors
1) kextload: extension /System/Library/Extensions/AudioReflectorDriver.kext is not authentic (check ownership and permissions)
Type the following command in Terminal (each sentence is in one line):
sudo chown -R root:wheel /System/Library/Extensions/AudioReflectorDriver.kext

sudo chmod -R 755 /System/Library/Extensions/AudioReflectorDriver.kext

sudo kextload /System/Library/Extensions/AudioReflectorDriver.kext

2) If you have problems with the choppiness of the sound and adjusting the value in /usr/local/bin/a2dpcast aa-bb-cc-dd-ee-ff 20 did not help, you can try to unload kext and reload it.

However, according to Tim, a2dpcast-0.3 shouldn't give you this problem. So you should not try this solution unless you have tried all other options.

Type in the following:
sudo kextunload /System/Library/Extensions/AudioReflectorDriver.kext (you may need to do this twice)

sudo kextload /System/Library/Extensions/AudioReflectorDriver.kext

3) a2dpcast does not work with Motorola S9! If you have S9, you best bet would be to use Softick Audio Gateway for Mac OS which is mentioned here.

You will see the following message in Terminal when you run /usr/local/bin/a2dpcast aa-bb-cc-dd-ee-ff with Motorola S9.

Found audio device "Motorola S9"
No such audio device 'Stereo Bluetooth Headset'. Using System Default.

Using audio device "Motorola S9"

sample rate is 8000, channels is 2
discover : received
SEID = 2
SEID 2 : MPEG codec
SEID = 1
Sent set configurations command
set_config : accepted
open : stream channnel
open_stream : ok
start_stream : ok
mtu = 672

frm_len = 2
6000 bytes/sec, hdr.sampling_frequency is 0
Transmitting A2DP, press RETURN to stop.
Bus error

Notice the bus error. If for any reason when you use your bluetooth stereo headset (other than Motorola S9) with a2dpcast and Terminal gives Bus error, it probably means your headset cannot use method (2).

4) Here is a list of supported and unsupported bluetooth stereo headset available from another post on David Connolly's blog.
Working (intel mac):
Motorola HT820
Griffin Bluetrip
Plantronics Pulsar 260
Plantronics Pulsar 590A
Jabra BT 620s (1 report of performance problem, Other reports of success)
Sony DR-BT22A

Not working (intel mac):
Sony Ericsson's HBH-DS970
Omiz Combo BT headphone
Motorola S9
Motorola DC800
Jensen WBT212

Enjoy A2DP on your Mac!