What you have not done is actually... what I would have done first to start with!
To make sure it works and works alone.
Mixing is suppose to work now, better, but as OWC found earlier, mix and match requires DIMMs that will.
There is more in depth on MacRumors about ranking, Registered and much more about using 3rd party and what to look for and does or does not work. Which is nice, they try and tend to keep everything in one place, one thread, easy to find and read.
And Newegg price isn't really different than say buying from MacSales.