Ah, okay, Adimon. Thank you for the reply. I'm afraid I was asking for selfish reasons. I've owned my DMA-90 since I purchased it new in 1995 or so, and each and every time I use it, I am so terribly thrilled with it: its appearance (its relatively tiny size), how quickly it warms up (and how, not being Class A, it doesn't throw off much heat and dramatically increase my utility bill), and especially how it sounds (it is so accurate and discriminating, and its noise floor is so incredibly low)! Your 100S shares all these characteristics, too, I think. I'm seriously considering moving to some relatively inefficient ATC speakers, which of course means I would need to upgrade my DMA-90. And, frankly, I'm conflicted!
Good luck with your upgrade. I hope you'll let us all know how it turns out.
Regarding your post #3, if I were you, I would upgrade the DMC 15ss to the 30ss. My reason is that based on your post #5, it seems like your power amp and speakers are already well matched and in my experience, using a better Spectral preamp or linestage always results in more improvements.