got rid of shadows on portraits, but now subject too dark - help?

Hi, I have been taking portraits of subjects against a white
background. In an attempt to get rid of shadows, I have started
lighting the background with 2 tungsten 500 watt lights and then using
fill flash on the subject. This has worked beautifully, except that
occasionally my subject ends up a little dark and not contrast-y
enough. I've been fixing this in photoshop, but wondered if I used
lesser lights on the background (say 250 watt?) I might get the
subject a bit brighter all the time? I am shooting digital and
converting to black and white, so I don't mind about the tungsten
cast. Any help would really be appreciated. Thanks! Lynn