Large Advents: Recommend Updated Tweeter

I have a used pair of the "New" Large Advent from 1979.They are temporary, until I can make up my mind about new hi-end speakers. Around 1979-80,the "New" Advents adapted a mylar tweeter which claimed to go 12Khz.(The "three position switch" on the back of the cabs only makes them brighter and a bit louder) I am running them with high end electronics,and they sound very good and are clean and accurate, except for the mid to high frequencies; I can hear the mylar tweeter's limitations which often sounds like it is straining. Also, the limitations of this driver especially when used with better electronics, seems to limit the depth and width of the soundstage and the solidness of the imaging. Therefore,has any one attempted to modify this speaker with today's updated tweeter, or know some company doing mods on the Advent to greatly improve the areas I mentioned??? I know little about the electronics of speakers, but know that if you change one driver you may have to change the crossover. I am not looking to drop mega bucks on this project, nor do I want to change the fundamentally clean and neutral sound Henry Kloss magically created with this speaker. But, its seems that a few changes could make this speaker much better in terms of imaging and high end extension. I have heard alot of speakers in the last 30 years, and the Large Advents lit up with good electronics stomp all over many of the most respected mid-fi to even modestly priced hi-end speakers out there. All input welcomed. Thank you, SJ