In an approach that's similar in some respects to the Tonian Acoustics TL-S1, the Sonist Concerto 4 ($5895/pair) marries dual, proprietary, 8" treated-papercone woofers to a Fountek NeoCD2.0 ribbon tweeter for a claimed frequency range of 27Hz40kHz and 97dB sensitivity.
While Sonist had a few tube amplifiers on hand, we listened to the Audion Sterling Silver EL34 Anniversary integrated amp ($3499), the Wyred for Sound Sonos sample-rate converter ($890), which converts i2S into 96kHz, up-sampled S/PDIF, and a Wyred for Sound 32-bit DAC ($1499). The DAC has a defeatable 32-bit volume control, 2 coax inputs, 2 Toslink inputs, 1 AES/EBU input, 1 balanced i2S input via HDMI cable, and a 24-bit/192kHz asynchronous USB input. All cabling was the Cable Research Lab Bronze Series.
Ribbon tweeters are seductive fragile beasts and when they can be coerced into playing in-sync with lower-voiced drivers, the combo can make for some smooth operators, which is very nearly the exact and only thing I noted about my Concerto listening experience"smooth."