Hi Steve. I took a cursory look at the overdrive info on your website http://www.empiricalaudio.com/products/overdrive-dac and user manual. I couldn't find anything about the type/kind of D/A chip(s) or whether or not your technology is considered delta sigma, multibit r2r or something else. Please advise.
I decided to use a Analog Devices delta-sigma, but only because I can select the digital filters for it rather than it selecting the filter for me. I cannot seem to get the HF transient response from older ladder chips that I can from newer delta-sigma chips. It also supports 24/192 PCM, as well as allowing for reference voltage-based volume control.
I previously offered a tube DAC design using a ladder chip called the "Spoiler". It was very musical, but ultimately did not deliver on the accurate HF sonics that I'm after. It also required hard-to-get expensive NOS tubes to sound really good.
The only other option is to design a ladder DAC from scratch or in an FPGA. I don't have the bandwidth for that unfortunately.
BTW, audiostream will be reviewing my new SX DAC soon.
Steve N.
Empirical Audio