Between a true HID projector vs. halogen projector w/ HID bulbs in it there is a HUGE difference in beam pattern, cut-off sharpness and color. I've retro'd bosch e-46 and e-55 projectors before, and even though they aren't TSX projectors, the light output and cutoff was already exceptional. If you're going to retro, do it right.
But if you aren't doing a projector retrofit, why even use an OEM D2S bulb that's gonna flop around in your headlight housing? You could just get an HID kit with rebased bulbs for your silvia headlight so it's a direct plug and play. HID kits are dirt cheap nowadays.
Check out this place: $39 bucks for any standard 35w full HID kit, any color, any bulb size, AND lifetime warranty. It's tough to argue against that.
http://www.ddmtuning.com/hidkihidbuhi.html