It's pointless fitting any kind of new bulbs to 20 year old xenon plus with a cracked and yellowed diffuser, its like trying to revive someone who's been dead for many years

no matter what bulb you fit.
Getting xenon headlights is the way to go, they are 100% interchangeable with Xenon Plus, light output is many times better right off the start (comparing 20+ year old x+ and x) and they can also be fully refurbished by having the lens reflector and the main reflector re-silvered. If you ever take your car abroad, they also have the toggles inside to switch the beam pattern to European roads. Even halogens are better than Xenon + sorry but that is just a fact. However if you compared brand new halogens, x+ and x, x+ would probably come out on top but the diffuser would yellow after few years and xenons would be number 1 again.
That's what I've done and arrived at for the best solution, having tested and stripped apart all D2 headlights.