Coreaudiod stack shots freeze audio causing major issues for music performances

Question

Dear all,
I've been experiencing a very annoying issue : is several applications (Itunes, Mozilla, Safari, Ableton, etc. - everything that does audio) is get occasional, irregular freezes. The audio would freeze for about 20 sec, videos that are playing would freeze too. After this 20 sec freeze thing continue normally. If for example a track plays in iTunes and freeze at the 1'00" mark, it will continue playing from there after the approx. 20 sec freeze is over.
Other apps opened in the background (text editor for example) remain functioning.
The issue is hard to repeat and irregular. I work professionally with audio so this is a nightmare - it ruins recording sessions and I need to be able to count on faultless, stable playback for live  performance.
OS is 10.8.5 - I cannot upgrade to 10.10 at this moment since my firewire audio interfaces (Mackie Onyx + Motu Ultralite) will most likely not be compatible with the newest mac OS (as stated on the audio interface manufacturer's website).
Macbook pro model is late 2011, 2,4gHz processor, 8gb Ram
This issue happens both when using the internal soundcard and when using external audio interfaces.
Every time this freeze happens,  a list like this appears in console :
" coreaudiod : Disabled automatic stack shots because audio IO is active"
" coreaudiod : Disabled automatic stack shots because audio IO is inactive"
" coreaudiod : Disabled automatic stack shots because audio IO is active"
" coreaudiod : Disabled automatic stack shots because audio IO is inactive"
" coreaudiod : Disabled automatic stack shots because audio IO is active"
" coreaudiod : Disabled automatic stack shots because audio IO is inactive"
(sometimes the list of enabled-disabled is longer)
troubleshooting i've tried so far :
1) I have recently done a clean install of the OS, manually copying the necessary files and installing the applications. I was obliged to do this since my hard disk failed 2 weeks ago and my mac had become very unstable. I've been working on 10.8.5 for a long time and haven't encountered this issue until after the clean install.
2) updating all necessary firmware
3) updating adobe flash
4) creating a com.apple.audio.ServerSettings.plist file  with xcode and placing it in the library/audio folder with this content :
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>AllowStackShotsDuringIO</key>
  <true/>
</dict>
</plist>
a tip i found here : http://apple.stackexchange.com/questions/91297/coreaudiod-spams-system-log-enabl ed-automatic-stack-shots-because-audio-i… After doing this i didn't have the problem for 1 whole day, afterwards the same issue popped up again.
5) manually quitting the coreaudiod process in activity monitor and restarting - this also seemed to help for a while but didn't last
Any hints and help are extremely welcome - I need this issue to be solved asap since i need to be able to depend on a stable audio environment for professional reasons.
Thanks a lot in advance,
K

Answer 1

Oh and I also tried :
* P-Ram reset
* repairing permissions, verifying disk and hardware diagnostics - no apparent issues there
thanks
k