Matthias Michael Beckmann - The5stringCellist

The official YouTube channel - Matthias Michael Beckmann // #The5stringCellist

Matthias Michael Beckmann ranks as a pioneer of the cello: playing a unique 5-stringed cello with a descant E string and a range of five octaves, he is the first musician to perform the entire cello repertoire on a 5-stringed instrument.

He teaches a class for 5-stringed cello and holds master classes at home and abroad. 
https://www.matthias-michael-beckmann.com/privates-beratungsgespraech/

"Matthias Michael Beckmann's playing is both elegant and inspired; his tone is rich in subtly differentiated colours, his intonation flawless. The high notes, radiant yet mellow, that he coaxes from his fifth string are truly breathtaking..." (international press critique.)