What is the modern equivalent to the L1090?

Not sure there would be a " modern " equivalent. The ADS Analogue Digital System speakers were really good in their time. I had a pair of ADS 610's, clean and accurate. That was back in the 70's

Spendor or Harbeth!

Those old ADS speakers were real gems. I still have a pair of 1290's in my HT system. I agree it may be hard to find a modern equivalent. You might want to help us out with what your 1090's do that you really like and want to capture in a current design. For instance, there are two aspects of the old ADS line that really appeal to me. The tight, fast bass, and the overall timbral accuracy. In those two respects, I find them similar to Magnepan speakers. In fact, since 1984, I have used only ADS or Magnepan speakers in my main rig.

What Brownsfan said!!!

I had a pair of ADS L1090s from 1987 to 1996. Since then I have had a couple of pairs of Mirage speakers and liked them a lot; I still use a pair of M5si's in my HT rig.

BUT… I started craving that neutral, articulate, room-filling sound, and Brownsfan is onto something here. I now have a pair of Magneplanar 1.7s, and in spite of the wildly different form factor, the 1.7s do a 2013 version of what I liked about the ADS: They are neutral, extended, room-filling, and are excellent at ranging from solo acoustic instrument or voice all the way up to full scale orchestra with chorus.

Although the L1090s were phenomenal in 1987 when I bought them, I'll take my new 1.7s over them. They are even more resonance-free and noise-free, even better at sorting out the complexities of large scale orchestral + choral music, and have a relaxed ease of presence I find even more engaging and endearing. Tonal balance and bass extension are pretty similar as well.

They are even about the same money. L1090s in 1987 retailed at $1100/pair. Adjusted for inflation this is equivalent to $2186 now. Today a pair of 1.7s with optional aluminum trim retail at $2100.

I bought a pair of L810s new and owned/enjoyed them for 20 years. Over the next 5 years, I "upgraded" several times but was never fully satisfied with my speakers again until I picked up my current Aerial 9s. Mike Kelly who is the owner/designer at Aerial, is the same guy who designed the L810s. If I ever upgrade again, I suspect it will be to Aerial 20Ts.