maybe
You could give it a shot... I tried to do the same thing. I have the Belkin system, and the problem is it only broadcasts between 88.1 and 88.7, and where I live, all those frequencies are taken.
The other problem is that yes, it can block out very very very weak signas, but the stronger the signal it tries to block out, you will hear hiss. And regardless, the sound quality will most likely be sub-par.
I would recommend, if you really want to use an FM broadcaster, get an iTrip. I believe they can broadcast over a larger range. I couldn't get one because when I ordered they had a long backorder and I needed it for a road trip....
That all said, if you want to connect them and get high quality sound, look in to finding the right cables and do it by wire. Old School, but still more reliable I'm afraid.
Hope that helps.
Good Luck!