I was having this trouble a week or two ago and still haven't resolved the problem.
Until recently I ran RTTY on my Icom 746Pro with a Kantronics KAM PLUS TNC set up for FSK keying. The TNC alway gave me intermittent problems so I decide to switch to WinWarbler's MTTY engine for transmit. I am using a Tigertronics Signalink USB interface for keying the transmitter via the 6-pin data port.
I cannot seem to find a WW setup that works properly. With WW set up to put the rig in RTTY mode I can key the rig and hear the audio but only get a carrier. No other tones.
If I switch the settings to LSB Digital I can apparently key the rig, but hear no tones in my speaker. It appears that unless I set the rig up in RTTY mode only the wide filter is usable. The narrower filters are not centered around the mark and space indicator lines in WW. What am I doing wrong?