Yes, the Essence ST has the Precision clock tuning feature, I guess it helps for sound (music) quality.
Just know the STX (PCI-Express) is cheaper then the ST (PCI) and PCI-Express is more future proof.
The analog 7.1 speaker upgrade for the ST is around $60-$70, but as your into music, you really only need analog 2.0 or 2.1.
The E9 and Essence ST (& STX) use the same T.I. 6120A2 headphone amplifier chip.
I guess get the Essence ST.