Hi,
I made an FM stereo transmitter using the BA1404 and it works ok, but the sound quality is poor and my stereo has a hard time picking up the signal and its only about three metres away, if the single isn't strong enough or if there is any slight drift it will drop out, the stereo transmitter uses crystal lock, so my stereo must be very fussy on the stability of the signal it receives. I have no trouble picking up the signal with my clock radio which is quite a distance away, as well as my car stereo but the signal is week.
These FM transmitters can be very touchy, I think using a transmitter with crystal lock in my experience is the way to go.