I have an older Panasonic video camera with a 3.5 mm stereo mic input.  I want to go out from a mixer into the camera.  How much attenuation is needed?  I see products that are 50dB (Shure A15LA Line Adapter) and others that are 25dB and 35dB.
Any product recommendations from experience?  I want to be able to mix the output from my audio interface with that of a microphone and keep the “audio” stereo (i.e., not mix the mic on one side and “audio” on the other at the camera).
Dave
P.S. I set the internal gain on the camera as low as it would go and brought the faders down in Sonar and it was still distorting when I went directly out from my Delta 1010 into the camera.   

Not sure what you're attempting, but...  Here's two thoughts.
 
1)  I'm guessing the camera is expecting mic level so could you maybe send the audio out a side-chain like you would to an outboard effects unit?  (Stereo Send/Return)
 
..or..
 
2)  Send the audio into a video processor (I like Filmora, about $60 for a lifetime license with free upgrades) as a separate source from the video from the camera and then match them up?

This is what I ordered:
 
http://www.sescom.com/product.asp?item=LN2MIC-50DB&LN2MIC-50DB
 
I plan on going line out from my audio interface into a mixer.  What I want to be able to do is sit at my mixing desk and create a video speaking into a mic and mix it with the audio from a project in real time.  Sort of like an instructional video.  What I think I am attempting ... is to bring the mix of the mic and the audio out of my Mackie board and drop it down to mic level before going into the camera.
 
I don't do much in the way of video or even know much about it but apparently I am not the only person who needs the ability to go line level into the 3.5 mm (aka 1/8") mic jack on a camera.  The different attenuations (as far as I can tell) are just for matching different gear (there is a 25dB attenuator for going from a Zoom to a camera). 
 
I figure the 50dB attenuator is my best bet as I will be able to adjust the gain at several points before it gets to the camera.

You might get more results posting in the Sonar or Hardware forum.