As an amplifier, the ST(X) performs similarly to the E9, it is also based on the same chip. Perhaps you would get some improvement in distortion and noise, partly due to the better DAC of the ST/STX cards. I do not know how much, if any audible difference there would be in practice, though. But if you were thinking about getting the ST or STX, then it would have been best to buy that in the first place, and sell the D2X if you do not need it. Of course, the E9 is useful as a stand-alone desktop amplifier that you can use from other sources without the PC.