Since the USB Regen is blocking ALL power coming in from the USB source there is actually no point using ANY power before the Regen. Due to the capacitive coupling
inside the USB cable (negative interference between power and data since they all being very close to each other) there is however a good point having NO power before the USB Regen. Any improvements (if any) with iUSB and iPurifier2 in front of the Regen would be in the data and ground lines only. A short USB cable is also important. The only way for you to tell if it is beneficial or not for your sound is to try it your self. The outcome very much depends on your system and your own sound preferences.
Blocking the power AFTER the USB Regen is just as important. The reason is still the same, ie capacitive coupling. However, judging by the sound improvement by removing the supplied short adapter (which should have minimal capacitive coupling) I
guess that it in some way also reduces the capacitative coupling inside the USB Regen itself as well. Please understand that this is my assumption only. All I know is that here is definitely a great improvement blocking the power in the USB cable AFTER the Regen as well. However, when you receive your Konvertible Lite 160 you will find out the SQ difference your self. I personally love that cable!
I would recommend that you start simple with
Gemini (no power leg)>USB Regen>K-Lite160>DAC and after you have listen to familiar tracks you add the
iUSB>iPurifier2>Mercury and listen to the very same tracks. Choose what you think sounds the best in your system. However, I am not sure if Gemini have the GND wire together with power or together with data wires? If Gemini have the ground wires together with the power wires you will not be able to do the simple setup since GND is needed for the handshake....and no GND is not beneficial for the sound unless you are using a star ground and unshielded USB cables (K-Lite is unshielded but Gemini/Mercury is not).