Got the HA-50 as my first portable DAC. I'm currently pairing with the IE800 and iPod touch 5G. I'm liking the sound quality so far. My music seems to come out with much more detail.
Software-wise on iOS:
On my iOS devices it does not need the TEAC app. to stream sound to the DAC and so far I've played music through the default music app. and Spotify with no problems.
If using the TEAC app., note that it will disable itself unless the DAC is connected. I don't use equalizers so I can't really comment on this app's feature. The app. is able to see your iOS music collection as well as its own (http://www.teac.com/product/hr_audio_player_for_ios/). To keep it simple, it's just plug and play for iOS devices. No adapter needed nor app.
Software-wise on PC (Win7):
So far, I have only got sound to it from the TEAC music player app (http://www.teac.com/product/hr_audio_player/). I couldn't figure out to use it as a sit-in sound card for my PC which was disappointing. The app. works like a regular music player, you create the playlist by opening your .mp3, .flac, etc. files. I don't really see myself using it for the PC anymore since it can only play music files when paired with a Win7 system.
Very solid build. All metal throughout the main body and the side rails are nice since they provide some protection for your cable connections and against accidental touching of the controls. It is a bit heavier than I'd like, almost as heavy as a 5" hard drive. I was really worried how much damage it would take if I were to drop it since it was so dense.
I really like the knob since my fingers grip it pretty easily and it provides a bit of friction so you don't turn it too easily. When charging with the barrel plug cable from USB 3.0, it does spark on touch. I'm not sure if this is bad or not. It's probably due to the higher amount current available via USB 3.0 vs USB 2.0. When using USB 2.0, it's doesn't spark, at least that I can notice.
With the sound, I do notice some noise pass the 60-75% volume level and when I my iPhone 5S nearby or strapped to it, I can hear the radio noise generated by cellular signals.
Also as mentioned before, I do notice my iPod's battery drains much more quickly when paired with the DAC then without. Whenever I connected the lightning cable the iPod would think that the DAC was a power source for a brief second. The DAC's power status also flickered during that brief second. Not sure what's going on there.