Hello!
How far behind are we talking about? The internal audio buffer that FamiStudio uses is approximately 3 frames, so the sound shouldnt "lag" more than 3 frames (~45ms) behind the yellow line which is very short. I'm assuming you have way more than this otherwise you wouldn't be reaching out! :)
On my home setup, I have found things like Bluetooth headphones to add a huge amount if lag (on everything with audio, not just FamiStudio).
Could you tell me more about your audio setup so we can diagnose this?
Thanks!
-Mat