If your ceiling height is about 2.4 meters (8 ft), and if the room does not have any openings to another area, then a GX-2 might be overwhelming when the lid is on full stick. Especially the treble might sound shrilling and disturb your ears.
I will just provide the relevant part from the RX series voicing manual on pre-voicing done at the factory. Probably that might also be valid for GX series. I am not sure though.
"Pre-voicing. Kawai hammers are pressed for high compression of the felt. This compression should remain unchanged under the strike point, where it will give brightness and power during Forte passages. Some of the tension in the shoulder areas is released by deep needling the hammers in the factory.
This deep needling is done in two stages in the Kawai factory; the first is done mechanically just prior to mounting the hammers on the shanks. Sample hammers are tested for hardness and rebound, and the shoulders are deep-needled by machine accordingly. The shoulders are then deep needled again in the voicing department according to their sound. It is not normally necessary for the hammers to be extensively deep-needled on the shoulders once the piano leaves the factory, although some deep needling may be called for to increase sustain or improve the sound of hammers that have been re-shaped."
Are you buying this piano unseen? Did you try a GX-2 in the show room?
IMO, it might be better to do the final voicing in your room, after the piano settles down in its new environment.