Although the PD is great a power hungry IEM will always benefit from a pure dedicated well designed powerful amp. While the amp in the PD is great, and even if the IEM does not seem to need an amp, adding an amp will add punch and take the load off the PD's amp and extend the battery life as you are not using the PD to drive anything only pass the signal to a more dedicated source. So if you have an amp try it and see, you will gain the following if anything:
1. More gain and control on the volume. R[COLOR=424242]esults in music that’s stronger, clearer, and not prone to strain or distortion at higher volumes.[/COLOR]
2. Extended battery life and performance of the PD. ( I rather change a batter in the amp than in the PD as it does not look like it was designed to have the battery replaced, not sure yet)
3. Added punch and possible better bass response as a dedicated amp will have bigger or better caps on the signal line and battery than the tiny PD.
4. A Class A amp will sound clean and clear with more authority than a Class B amp, which is what the PD is, of course the line out is still Class B on the PD but I rather do a Class B to Class A signal than Class B to Class B.
5. You would be able to drive larger cans with a dedicated amp than the tiny PD, if you have larger cans rather than IEM's.
6. If you are driving larger cans the PD's run time will be shorter, how much not sure.
7. A[COLOR=424242]mplification is heat; an amp needs room to dissipate this heat, even though the PD does not appear to give off any major heat, there must be some. With that said, I again rather have the PD be more of a signal out to an amp that is dedicated and designed to run and have heat. This in theory should make the sound better, but if it's detectable is hard to say.[/COLOR]