I have read this very long thread. Very happy it gives so much information. Here is something I find when checking chinese information site about Xiang Sheng DAC01 and Tube Magic D1.
Here is a person who is selling modified Xiang Sheng (old Maverick Tube Magic D1) with NE5532 OP-AMP, and 6H3n/5670 tube (you can select which tube when you roder your modification).
FInally, he also offers to make interesting modification changes to the earphone output by wiring it through the tube as a buffer. (at bottom of page - option 3A/B)
He has also said via email, he can also remove original earphone protection circuit which makes sound even better in his opinion.
When I ask why he makes these modifications, and how sound quality changes - he says original Xiang Sheng design was too bright and forward on earphone output and his modifications make the earphone sounds more mellow, but not lose base or midrange definition. The DAC part he says has better solid bass after tube change and some component change.
Here is site in chinese: