Speakers for Leben CS 300XS

I would choose between any of the Devore models and some Coincident Technology models. They all are easy to drive.
The Coincident Technology Triumph Extreme monitors are 94 db and sound excellent. They also make a passive subwoofer that also acts as a stand for the monitors, making for an exzcellent combo. Of course, the more expensive Coincident floor standers are excellent.

Another great floor stander is the Vaughn Cabernet. At about $8,500 delivered it is an outstanding value and an excellent performer. There is a great review on it online in Stereomojo.

Greg

Another vote for DeVore Super 8's.

Tonian Acoustic TL-D1

I have Devore Super 8's paired with my 300XS in a 15x15 room.
It is a incredible match.

Living Voice IBXR2's

When I've heard Leben and Devore together on several occasions, I've had to stop myself from reaching for the credit card. They sound sublime together.

I am running Devore nines...Bliss

Howdy...agreed, Devores would be great.
Skip the Harbeths this time around. You really need more power (and I love the Harbeths)

One you may not be familiar with is the Totem Sttafs---a thing of beauty with the lil Leben.

One other thing, PLEASE do not mate the great Leben with any Dynaudios.....blah...

Any of the Devore Fidelity speakers would be a great match.

Merlin TSM-mm

Harbeth C7ES3.
Unless you have a very large room, don't worry about the low power, or the speakers sensitivity.

Musical Affairs Grand Crescendo

Audio Note...any model