Hi!
I've been using the PM-3's and the HA-2 for about two weeks now.
Last week I attended a conference in New Orleans, and thought it would be an ideal way to test the new gear on the road, in planes, etc.
First thoughts are that the combination of the HA-2 and PM-3s are a dream combo. The PM-3 had almost no sound leakage, and I asked my fellow passengers to listen for leakage and they said they couldn't hear anything, even when I cranked the volume, and the ambient noise cancellation was very good. As for comfort, they were just wonderful.
Using the HA-2 took a different turn. I don't really have much music stored on my Samsung S5, or my older iPad Retina. So, I brought along a Seagate Wireless Plus drive with a built-in hotspot. Using the older 40 pin iPad cable to the HA-2 worked great, and I streamed high-res audio FLACs to the iPad, and then played them using Capriccio to the HA-2. Worked fine.
I also tried with the HA-2 rubber banded to my S5, used the small mini to mini USB connector between the phone and HA-2, and played a few files on my phone (Rolling Stones - Official Bootlegs, Brussels, and Los Angeles concerts) and they sounded great. Then I used the browser on the phone to connect to the Seagate Wireless Plus and once again the files played just fine.
I had a bit of worry that I damaged the phone cable for the PM-3, as I couldn't get both channels playing, but it was a "Doh!" moment. I had inserted the wrong end of the cable into the PM-3s, so once I figured it out and plugged the proper side of the cable into the headphones all was fine! My bad!
By the end of the flights, I found myself tossing the Seagate Wireless Plus drive into my backpack, and the phone/HA-2 rubber banded combo into my jacket pocket and all was well, high-quality music on the road, with TB's of tracks to choose from.
As for hiss, I simply had none. Even in a dead quiet hotel room, using the PM-3's, I had the phones on my head, the HA-2 cranked up, but the battery had run out on the Seagate unit, I kept checking to see if the green LED was still lit on the HA-2, as it was so quiet with the phones on and no source audio. I've not tried the HA-2 with IEM's, and I have quite a few to choose from, so will see if I can hear any hiss with them. But for headphone use the HA-2 seems dead quiet. I did try them with Oppo PM-1 and PM-2, and several Audio-Technica headphones, and same results, no hiss.
The unit does run a bit warm, but this is expected for an amplifier of this design. Everyone who saw the combo asked to listen to them, and once they did wrote down the Oppo website in their phones.
I have the white models, which are quite cool looking, but I think I preferred the black design a bit more. Why the white models? My wife and son said "Get the white ones, you have so many black headphones already" so.. white model it was!