Poweramp is not really a substitute for Voodoo. It's a software media player that offers better EQ options than the native android media player, whereas voodoo is a hardware-level hack that unlocks features of the Wolfson DAC chip present in some players to improve SQ.
Poweramp is great if you're stuck with a GSII, but all it really does is upgrade the SQ from "horrific" to "bad". You'll still wish your music sounded better.
I guess if you carry around your E7 it's a moot point because you'll be bypassing the GSII's internal DAC in favor of the external DAC, so you should make sure that works. Not all external DACs can get a usb audio signal from every device.
Also, since you mention Euros, be careful when you do research about US vs EU variants of phones. For example, the international GSIII got a Wolfson chip, whereas the US version didn't.