Power requirement for ADS L-1290?

Also,

90db @ 8ohms is actually quite efficient. But I agree that they would do better with at least 100wpc or more. I dont know about the impedance dips as I have never seen them measured. Perhaps someone else can comment.

I can answer this pretty well since I have the same speakers and I started out powering them with a 60 wpc Denon receiver. They were OK, but then I purchased a separate Denon Power Amp POA-5200 (125 wpc) and the sound difference was very significant. Much deeper and richer bass and mids. Much more dynamic in terms of the clarity and volume of different instruments in the music. I think you'd be much better off with more power for those great speakers.

A pair of the L-1290/2 speakers were just given to me and they are in good shape. The oak cabinets are in excellent shape, but one midrange was pushed in and has what looks like shag carpet fibers on it. Perhaps it had fallen down on some carpet. I wasn't able to remove the midrange metal piece from the cabinet to try and push it out from behind, but was able to restore most of the shape of the dome by pulling with some masking tape.

I have a pair of DCM QED 1A speakers that I bought in 1985 driven by a Denon AVR-1910 receiver (90 watt x 7). My QEDs are not terribly efficient, being transmission-line technology, perhaps 86-88 db SPL, but the sound quality and dispersion continues to impress me even after shopping for a second room modern bookshelf/sub setup last year. The L-1290s are almost the same vintage as my QEDs, but cost 50% more back in the day. I was thinking of using these as rear surround speakers, but a Stereo Review of them from 1984 measured them as 4 ohm and 90 db SPL. I worry that my receiver will be able to drive them with their low impedance along with my QEDs and volume matching them since they are more efficient. I'll have to go through my receiver settings and hopefully I can adjust the rear volume separately.

I swapped cables with my QEDs and they sound awesome even with the slightly deformed midrange and the tweeter above also had some fibers on it. I listened to my favorite reference CD, Dire Straights - Brothers & Arms 1985, mostly track #4 Your Latest Trick. There is more detail and clarity than my QEDs - I can separate the symbols from the other high frequency sound which blends in and is less transient on my QEDs. The saxaphone can get a bit tiresome harsh at reference levels on my QEDs, but not the slightest on the ADS. The bass is also fuller and contributes to a larger overall stage presence. These speakers impressed me enough that I decided to replace my QEDs with them as my mains and I've ordered 50 foot 12 gauge cables to hook up my QEDs as surrounds. They are pretty closely volume matched to my QEDs so I think the SPL db is close even if they are lower impedance. My receiver does have separate volume levels for each speaker.

I've had a pair for years
Originally with mono blocked NAD 2155's ( 125 wpc )
Then Emotiva UPA-1's ( 200 wpc )
This week I changed to high current Emotiva XPA-1's ( 500 wpc )
Each increase in power made a pretty startling inprovement