Chris, you and I have the same digital front end. Yet, I find this combo to be wonderfully musical with great microdynamics and full extension on the top and bottom. Very "emotionally" involving, not laid back and distant at all.
I do use the MBL reference clamp instead of the one that comes with the 1621 transport, the tubes in the AA DAC are Amperex long plate D-getters, and finally I use a Stealth Sextet cable. Would you please share if you have ever experiemented with the upgraded clamp and what tubes and cable you use in your system. Maybe, its these other factors that are taking away the dynamics/emotional aspects that you say you are missing in your rig. I have heard most of the very high end digital gear and still have not heard anything that makes me want to replace either the MBL transport or Accoustic Arts Tube Hybrid DAC in my system.
I do use the MBL reference clamp instead of the one that comes with the 1621 transport, the tubes in the AA DAC are Amperex long plate D-getters, and finally I use a Stealth Sextet cable. Would you please share if you have ever experiemented with the upgraded clamp and what tubes and cable you use in your system. Maybe, its these other factors that are taking away the dynamics/emotional aspects that you say you are missing in your rig. I have heard most of the very high end digital gear and still have not heard anything that makes me want to replace either the MBL transport or Accoustic Arts Tube Hybrid DAC in my system.

