Speakers that are good with tubes

@lewl28 

Tubes do not like big swings in impedance

What @hilde45 said, sensitivity yes it is important but the speakers with tubes (in general) won't shine if there is either an impedance difference or in general impedance under 8 ohm.

I do have a pair of Klipsch P37F, nominal impedance 4 ohms, only my Atmasphere MA-1's were capable (@120W output) to get them to sound decent. Other tube amps couldn't do it well. The day I put a solid state amp with those speakers there was no turning back, these speakers are made to match a SS.

Note that I love tubes, I'm not comparing tubes to SS

Try whenever possible to look for speakers that are at 8 ohms and over.

James Romeyn / Duke LeJeune / Hans Looman were involved with a recent design presented at CAF of a phenomenal speaker which if I'm not mistaken will be very friendly to tubes but you would have to look more into the details.

Tubes and horns are lovely together.

Do buy the Speakers first so you are 

not painted into a corner.

+1 for the DeVore O/96 

Here is the "tube friendly" speaker article....

https://www.dhtrob.com/overige/tubefriendly_lsp_en.php

Many of the pitfalls users are describing that torpedo  tube amp performance are just poor speaker design.  So I'll add to my suggestions:  Buy a well designed speaker.

It does not have so be 8 ohms or above.  My speakers are 4 ohm, but they are very, very flat and very well designed.  I bought them to use with an ss amp.  The first time I heard them with a tube amp, I promptly sold the ss amp.

Jerry