OK, a bit of an update:
I have a Musical Paradise D2 DAC here and I have a direct and highly beneficial mod developed for it. In stock form, with 6922 tubes and this unit has AKM DACs, it is good but not great. It just seems a bit forward and somehow lacking in overall cohesion, soundstage and depth.
I first studied the circuit, using the 6922 in this case and the power supply. I decided that the operating bias point chosen by the designer is not ideal and I have addressed this. The result is VERY good and makes a BIG difference!
The power supply design is good, but simple. High voltage is used, presumably to allow for the use of many different tubes. I like the 6922 tube and so my mods for this DAC will focus on the use of this tube. The transformers are isolated from the audio circuitry via steel enclosure which is good and a choke is also used in the HV supply. My next step will be to replace a simple RC main filter with a discrete high voltage regulator. I expect this will make another significant difference in the performance. When I am finished, I expect this DAC to sound FANTASTIC!
RE TEAC designs. I have looked at their offerings and they do offer good promise! I am continuing to study them.
RE the Universal Mod box, it is much more than a tube buffer. It would essentially be the mod analog stage that we install in our existing Oppo 205's, or very similar, but will be in one box, including the supply. It will provide analog filtering, gain and buffering and possibly include a volume control and analog input. As such, it could potentially serve as Digital source mod and line stage to the amp. The digital mod input would ideally be a low level signal, post DAC output, before analog filtering and stock op-amp circuitry. Our mod box would take this signal and provide filtering, gain and buffering. The digital source would serve as digital processor, but would hand off analog duties to our mod box. This would involve a minor change to the source, providing a stock analog stage path to its stock outputs and a switched output, that takes the lowest level signal after the DAC, out to separate outputs to feed our mod box.
I hope this all makes sense and gives you all an idea of the direction that we are pursuing. I am still looking for a good candidate for the Universal Mod box (a better name to follow...). Ideally a DAC with DSD, Roon, MQA capability, etc.
I will announce mod offerings for the Musical Paradise DAC 2 for those who are interested. This design offers tremendous value for the money and I believe can be made to be great, with a few simple and cost-effective re-design and changes.
Thanks and I look forward to hearing more from all of you.