I have Altec Flamencos and recently asked for some advice on amplifiers that you might find helpful. Coincident Frankensteins and Music Reference were recommended for my speakers as well. Also Atmasphere thought that his class d monoblock amps worked well with his similar high efficiency speakers and should be a good pairing for the Altecs.
@alexberger gave me the following useful info regarding amplifiers and crossovers:
" I have experience with Altec 604E that has similar sensitivity to Altec 846A. In the mid size rooms that I had 200-300 sq feet, 300B SET has enough power. I used McIntosh MC30 monoblocks (30+ watt), Marantz 8B in triode mode (20 watt), and 300B SET (6-7 watt). I also heard 2a3 Boothed monoblocks with my speakers and they were good enough in terms of power. The 30 watt McIntosh MC30 sounded great with my Spendor 2/3 speakers but with super sensitive Altecs it sounded rough and not as natural and refined as a 300B amplifier.
What is really important is that for a 300B amplifier it has to have a powerful driver tube like 6f6, 6v6 but not popular but weak 6sn7.
The strong power supply with a big and good quality capacitor.
If your room is not huge, I suggest you try Coincident Frankenstein 300b monoblocks or Aric Audio Super 300B SET. Both these amplifiers have powerful driver tubes, interstage transformers and good power supply.
There are a lot of information about crossovers for Altec on Jeff Day page. Jeff prefers Hiraga schematic crossover for his Altec speakers.
https://jeffsplace.positive-feedback.com/
https://jeffsplace.positive-feedback.com/%e2%99%ab-vott-system/