For the original design, you can use a barb fitting with a male connector on the other end that almost fits the keg post. A little JB Weld and you're set without all the extra hardware. Of course, it means you can't re-purpose the keg post after that....
How are you cooling the wort after the boil?
What temperatures are you fermenting the beer?
What yeasts for each of those beers?
It may be that you have an infection in your equipment and it transferred to the beer... Do all 3 beers have the same bad smell?
I agree with the others that...
You probably either over-pitched the number of yeast or fermented too warm. Make sure to keep the fermentation temperature in control (below 70F for most ales and below 50F for most lagers).
Recommend looking at this to help you understand possible places of where you are losing efficiency.
http://www.braukaiser.com/wiki/index.php?title=Understanding_Efficiency
This link helps you troubleshoot efficiency problems...
Sorry about not replying to this thread earlier. I kinda lost track of it since I was able to entice my friend into drinking cider instead of GF beer. I haven't done any experiments with regard to this.