Hya,
Don't worry, I've been pointing dishes for years with my PCs, always using dvb software. I know the display levels aren't accurate, but they work ok for me, I try to maximize on the weakest transponders. I've set motors up this way too. I had a cheapo satfinder when I first got into the hobby years ago but it annoyed me more than anything. It won't tell if you're pointing at the wrong satellite. I have never again used one.
It's good to know that the prof 7500 has a nice tuner capable of picking weak signals. But are you 100% sure it works in the way I tried to explain? To illustrate further - the Technotrend S2-3600 has a led, that will stay yellow when not locked to a signal, and turn green when locked. If I have say a dish that I manually, intentionnally move, the card will loose the signal, becoming yellow, and if I manually put the dish back to its place, the 3600 will not on its own become green again - ONLY when I tune to a channel again on the dvb player it will lock again the transponder and become green. So, it's impossible to move a dish pointing at the sky in an attempt to find any incoming signals with these cards.
If I get a suitable replacement I will sell the 3200, the thing is, I'm in Europe not NA...