Looking for new (to me) Speakers for Leben CS300XS---Devore, Harbeth, or Reference 3A?

“What would you do?”

I would take my Leben CS300XS along and audition all three speakers on your list. I wouldn’t do it any other way unless you’re buying new set of speakers with in-home audition return policy.

Chris,
@lalitk offers a very wise and doable suggestion.
I’m skeptical about the Harbeth driven by the 15 watt Leben however you have the fortunate opportunity to take your amplifier and listen for yourself.

No matter how well intentioned or thoughtful some of the responses you’ll receive here,   the ability to actually hear, the Leben with your list of speakers is the superior option.
Charles

I wouldn't let anyone bring their amp into my home and try it on my speakers before purchase. In fact, my system isn't an audition period for anyone. Learned that lesson long ago. 

I run my Ref 3A de Capos with a 4 watt Decware mini torii. Does it get concert loud, no but loud enough for a 12x20 room.