fully midi bass

You need a battery.

 

No you don't need a battery as the GK kit runs from the powered 13 pin cable from a Roland synth unit (GR-55,20 or VB-99).
The GK kit pickup is only an analog hexaphonic pickup where the 6 analog signals are fed to a synth unit for processing into midi.
The GK kit does not do midi itself.
The GK kit does not provide analog sounds either, but the synth unit such as the VB-99 or GR-55 with it's HRM modeling can use the hexaphonic signal to restructure different model basses or guitars.

 

If you want a midi only system, wait for the Fishman Tripple Play wireless midi to come out in a bass version.

 

Yes, you don't need any stock pickups, only the GK system will do.
The GK hex pickup fits right up against the bridge for best results.

Here is a site dedicated to such stuff,
http://www.vguitarforums.com/smf/index.php?board=82.0

Here is my 6 stringer fitted with the internal GK kit



It still has the stock pickups, but i don't use them.



I re-used the original rear knob for the GK-Vol controller, the two black push-buttons do patch up/down, the silver toggle selects GK/both/normal pickup.

 

Yes, with the VB-99 and GR-55 you can even use the effects within the Roland units.
The GR-55 gives me normal bass pickup, modelled bass and guitar tones and two independant PCM synths each with 910 built in sounds.
I use the GR-55 Expression pedal to mix between normal bass and the synths.

The GR-55 also has a USB memory stick which i use to play intro and song sound samples, triggered by the gR-55 pedals.

Here is a Roland GR-55 with Bass demo i found

 

The GR-55 does have a GK setup option for the RMC Piezo as used by Conklin.
I can't comment on what the RMC system is like, because i don't know.