So, do we want to keep the HPA-2 talk in this thread instead of moving to the 2014 M-Stage thread?
The new HPA-2 has increased power due to lowering the output impedance from 15 ohms to 10 ohms, which drives the transistors harder. The unit runs noticeably hotter, so be careful how you have it placed. I will be doing a comparison soon, but expect most of it to be centered on the DACs for the version with the USB DAC. The amp section is mostly the same parts.
I didn't see another thread, but would be more than happy to re-direct my inquiries to a more specific thread.