Hello,
on Siena Empoli route there are trains to Empoli and other to Florence (all trains to Florence stop in Empoli).
The trains to Firenze, usually, are pulled by D 445 diesel locomotives. Trains to Empoli are DMUs ALn 501/502 (Minuetto) or ALn 668. In the future also ATR 220 (Swing) will run to Empoli.
The effective type of rolling stock depends by the real situation (traffic, delays, maintenance, breakdowns), so program can be changed.
Other D 445 locomotives work in Reggio Calabria, Taranto, Treviso, Cremona, Torino (freight) and Cagliari.