I don't know if I can help, but I just set up my weather station doing pretty much what you are attempting.
24" iMac running OS X10.6.8 (so a newer OS)
Davis WeatherLink 5.10 connected via Weather Envoy.
Silicon Labs driver CP2102
Lightsoft Weather Center 2.11 (build 50)
I was running into the crashing and error problems until I read to check the 32-bit option. Then things worked fine. I did delete the newly created station folder and config.dat in user --> WLink between each try. That might help.
I find the libjspMacOSX.jnilib file in the Applications --> "Mac OSX WeatherLink" folder along with the WeatherLink application.
I only used WeatherLink to set the barometric pressure on the Envoy (as described in http://www.wxforum.net/index.php?topic=12936.msg125582#msg125582
.) I use LWC for everything else, and never even have WL running.
I hope that helps get things running for you. Pop in at MacWeather.net for a LWC specific forum to compliment the overall station and weather knowledge here at WXforum.