Stereo Tool

What preset get best results? Input Bufer,Output Buffer and Asio Buffer?

Presets are a matter of taste. For FM, I would go for the normal or even soft compression versions if you want quality. If you want to match the loudness of the big commercial stations (this may depend greatly on where you live), go for FM Loud or FM Extreme. Don't use FM Hot - it sounds unclear.

Assuming here that you're using the stand alone version: If your sound card supports ASIO, you can use it to greatly reduce the latency that Stereo Tool introduces (ASIO has about 10 ms latency vs 250 ms for non-ASIO - this is without any processing, the processing also introduces latency). If you do use ASIO, you can select which input and output ports you are using (all must be from the same sound card, unfortunately. This is a limitation of ASIO).