My Stealth Hyperphono cable is not suggested by the manufacturer to be broken in with a high level signal due to it's design. My cart is .5mv output.
WHat I have done in the past to break in phono stages is is that I made a reverse RIAA signal of white noise (and some music as a test that the levels are correct) I play this in quicktime or another player and set it to loop. I lower the output of the computer to very low, and also the output of the quickime player to very low. Between these 2 volume adjustments I can get the very low signal that mimics the output of a cart. I use the music track to make sure I am not overloading the phono stage.
I should probably try this combined with Alberts suggestion about making the din to RCA cable then I could set a slightly hotter signal that the cart would be outputting - maybe double .
If anyone needs the inverse RIAA files I have them in both mp3 and aif formats. email me.