Please recommend speakers for Cary CAD-300SEI LX20

Coincident or Soliloquy might be worth a look. I've heard the later model SEI (w/remote) w/Partial Eclipses & it was really good.

You got to hear the Reference 3A Veena speakers.
Its a tower version of the MM DeCapo.
The sound is much fuller and the bass is superior on the Veena's compared to the MM Decapo.
The Veena's sound very articulate on singled ended tube amps.

I have been shocked and pleasantly surprised at the experience I've had with a pair of Hyperion 938s mated with a conventional 300SEI. The system evolved without a great deal of pre-planning and really was thrown together initially just to obtain much missed tunes following a system liquidation. The synergy realized, however, has actually outperformed several prior mega-buck systems for pure listening pleasure.

My Cary has the upgraded caps, wiring, and volume attenuator from Cary and Sophia Mesh Plates. Tara Power conditioning and cables stepped up the Cary's performance to well beyond what I thought this amp was capable of. The Hyperions represent a 6 ohm load and are 90 or 91db efficient. Originally running a Sony 9000ES CDP, max output was occaisionally missed, however, a recent change to the EMM gear, with inherently higher output, has made volume a concern of the past and added an incredible level of holographic detail.

Again, it is absolutely mind boggling to me what this Cary is capable of throughout the frequency range. I can't speak to the other speakers referenced, but the Hyperion really turned out to be a sleeper with this integrated and has not short changed on bass extension.