Check out LB Audio systems. http://www.LBaudiosystems.com
The HB-DAC1704 dac uses the famous PCM 1704UK (R2R) dac chips in 4 or 8 configuration. You need at least 4 for a balanced design. 8 is the best.
The PCM 1704UK dac chip is considered one of the best sounding R2R dac ever made. No longer in production...
PCM 1704UK chips were used in some of the best CD players (ie. Simaudio Andromeda, Esoteric X-01).
The LB Audio DAC will compete with any big brand name DACs from 10K to $20K.
Good luck and enjoy!.