I can't imagine that it would be possible to use your own amp as that would negate any of the "special sauce" of the active design. Technically I guess they could have 3 sets of stereo outputs where each could link to a separate amp, then a special cable to sum it all together again before entry to the IEM. Obviously that's not a very feasible solution.
My PP6 (molded, not a universal demo) is stuck in China due to some Fedex "shipping exception" so hopefully that gets cleared up and I receive it soon.
Quoted from some impressions on another site:
"A potential saving grace for the design might be found in their offering the PP6 IEMs w/ an adapter cable to allow them to run off your own DAC/Amp combo. The IEMs themselves have no crossovers or other circuits other than drivers. So the cable, if done right, could be a saving grace."