'Chrome OS' Guest (No Sound)

[BooII]

My first foray into using virtual machine software.
Used hexxeh's website instructions to download and install VirtualBox.
His last 20 Apr 2013 virtual image build downloaded and installed to 'Chrome OS' named guest of VirtualBox.
Both were achieved without any problem.
The guest host 'Chrome OS' video functions but the audio does not (no sound).
Have tried all combinations of guest host audio 'Host Driver' and 'Controller'.
'Host Driver' options available are 'Windows DirectSound' and 'Null Audio Driver'.
'Controller' options available are 'Intel HD Audio', 'ICH AC97', and 'SoundBlaster 16'.
Have yet to add any additional host drivers or controllers to see if can find a combination that will provide audio.
As stated above cannot get audio using any combination of already available host driver/controller options.
Since video functions correctly there is no reason audio shouldn't too (considering video is more complex to get working than is audio).
What is thought to be required is configuring VirtualBox with the right Audio 'Host Driver'/'Controller' name combination to get audio working.
It may be totally something else causing the 'no sound' problem and the reason for this inquiry to determine whether someone on the forum has a solution.
Audio and video working on host, just audio not working on guest.

Setup:

Host system is Gateway SX2840 (2.93 GHz Intel Core i3 530, 6 GB RAM, integrated Intel HD Graphics, Intel HD Audio).

Host OS is Windows 7 Home Premium (x64) Service Pack 1 (build 7601).

Guest OS is 'Chrome OS' with hexxeh's build 'Chromium 28.0.1484.1 (Platform 4028.0.2013_04_20_1746 vanilla x86-generic)'.

VirtualBox (Graphical User Interface) version is 4.3.12r93733.