Wilmer, thanks a lot for your comments. I might go to church to do some confession about my greed someday.
You are right that I should not focus on the unnecessary functionalities (e.g. usb support, up-sampling), which are not essential to enjoyment of music, just like we should not care much about the re-selling values of a product. Maybe, I have been too old and too poor to care so much every cent I am going to spend. I am sorry to bother you so much and feel grateful for every advice you gave.
Since you are not willing to sell me any of your products anymore, I might stick to my poor Lite DAC and decade-old 20W tube amp this moment.