First of all, the stock 6922 tubes are not even close to most of NOS tubes. That's why the seller didn't include those with the DAC.
As I replied you in your LS3B preamp question, I didn't think there was anything wrong with your preamp's volume control.
How was the tubes packed? if they were shipped inside of the DAC then it is possible that they could damaged from shipping. The damaged tubes would give you pop and hiss sound. "Lifeless and weak" has more to do with tube character itself. Get yourself Some NOS Amperex or Siemens 6DJ8s. If you want a lower noise type ( I would usually prefer lower noise for DAC but they're less liquid sounding) then get yourself some NOS Amperex/Siemens 7308 tubes.
As I replied you in your LS3B preamp question, I didn't think there was anything wrong with your preamp's volume control.
How was the tubes packed? if they were shipped inside of the DAC then it is possible that they could damaged from shipping. The damaged tubes would give you pop and hiss sound. "Lifeless and weak" has more to do with tube character itself. Get yourself Some NOS Amperex or Siemens 6DJ8s. If you want a lower noise type ( I would usually prefer lower noise for DAC but they're less liquid sounding) then get yourself some NOS Amperex/Siemens 7308 tubes.