A3: So far, I have no problem. I bought a second hand from eBay in 2017. A4: You need an amp. The DAC does not have enough power to drive headphone. A5: I bought it at $800.

I have recieved mine, used one, yesterday. I really love it!

Thanks for every comment! I have DarkVoice, and its sound is dramatically improved after I upgraded the power supply system with iFi iPurifier AC, Weiduka power filter, and Pangea power cable. So, I am thinking about using iFi iPurifier DC with the THX 789. However, the result of the measurement...

Since the provided DC power supply is the swtiching type, what do you think if I change it to the linear type or use iFi DC iPurifier? Will the improvement be worth to invest?

Lucky me! What I did the first thing after receiving the e-mail this morning is order the THX AAA 789. Don't hesitate!