After spending quite a few years experimenting with various components, I finally have a system which satisfies me, so I thought I would describe it and explain why.
Speakers: Davis Courbet 4 (http://www.davis-acoustics.com/en/courbet-n4/)
Amplifier: Lavardin ISX (http://www.lavardin.com/lavardin-isE.html)
DAC: ECDesigns MOS16 DAC (https://www.ecdesigns.nl/de/info/mos16)
Source: ECDesigns UPL (with ElectroTos cable) (https://www.ecdesigns.nl/de/info/upl16)
The speakers are the latest models that the french company Davis has produced. They are floor-standing two way speakers, with a crossover at 4000 Hz. In the few reviews that have been published, they are described as "well integrated" with a natural, transparent, and cohesive sound. I feel they are particularily well suited to medium size rooms - living spaces which do not have the acoustic characteristics of dedicated listening rooms. I previously had Harbeth P3ESR (anniversary) speakers, and the Davis are IMO much better on all aspects of sound reproduction.
The integrated amplifier Lavardin ISX is well suited to these speakers, and is both dynamic and transparent. The volume control is very precise, and does not seem to degrade the sound quality in any way. A good power cable (I use TWL) is a plus. The amplifier is plugged in to a Daitron Isolation Transformer (the models recommended by J.Swenson for their ability to filter high frequency noise on the power lines), and I feels that adds a little plus as well. Lavardin is known for their implementation of "memory distortion" principles (see here, for example: http://peufeu.free.fr/audio/memory/). I don't understand the technical aspects, but I do feel the Lavardin is a very transparent amplifier.
The DAC and source, I will comment on together. The UPL reads wav files from USB keys, and outputs an optical signal. The UPL was initially using a standard Toslink interconnect to the DAC, but ECDesigns have developped a novel interlink called "ElectroTos", which basically consists in putting the LED on the DAC side. Its all explained here: https://www.diyaudio.com/forums/digital-line-level/79452-building-ultimate-nos-dac-using-tda1541a-744.html#post6031506