We make both tube DACs. One with the Sabre 32 bit chip and the other with the R2R board. The Sabre uses a single 6SN7 with a single rectifier (GZ34 - 5R4, etc.) and the R2R is a 101D direct heated triode design. They have similar sound characteristics, but the 101D is a much more sophisticated design.
Happy Listening.
Happy Listening.