How to go line into mic on a Video Camera?

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.   

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.