I have been using Liveresponse from Kayako for about a year and a half and I have been very happy but it seems to only fully support IE, It works in Firefox with the exception that no sounds play when someone is requesting a chat which is something that is obviously needed.

I also tried the trial of PHP Live and get the same results, no sound.

Help Center Live is out of the question for me at this time due to some security issues I have had with it.

Does anyone have any other suggestions?

Try contacting Kayako and maybe they have a patch to fix the sound problem.