General Magnepan Tympani 1D questions?

As a vintage audio listener and tweeker I am interested in any potential mods or improvements I can make to my first pair of 1Ds. I look forward to your responces on the following questions:

1.Any success adding tweeters? Brand, type and how did you do it? Are they even needed?
2.Minimal suggested tubed power amps? I am not a loud music listener but will turn up to concert level on occasion.
3.Crossover mods for single amp?
4.Other suggested mods?