I'm looking at investing in a ss amp kit of some sort and would like to get something that drives my he400s to their best, but also has spare juice to power more demanding planars that I don't yet own. I've built amps before and can do that safely, I just need some guidance on how to...

I've had HD580s for approaching 20 years and would really like a same but better upgrade, yet phones I've heard with more detail become more harsh, and to me the trade-off just isn't worthwhile.  I might be one those people that insist old gear is better, despite it being objectively worse...