^ The Sonica DAC cannot replace an HA-1, unless you're only using the HA-1's DAC section. The Sonica DAC does not have a headphone amp.
I've spent a lot of time with the HA-1 using various sources and consider its USB input to be a weak point. I've even gone on record in the HA-1 thread, long ago, saying that even the sub-$100, 96/24-capable Teradak Teralink X2 USB-to-SPDIF converter will improve the sound of the HA-1's DAC section by coming in on the Coax or Optical input, instead of directly into the HA-1's USB input.
I'd say it could just be my copy of the HA-1, but I know of some other people who have concluded its Coax and Optical inputs sound better. For a long while, I used the Coaxial output of the FiiO X5 DAC as my source for the HA-1's DAC section. Inserting my Uptone Audio USB Regen upstream of the USB input doesn't seem to help the HA-1's USB circuit. Using a Resonessence Concero - not as a DAC but with it set to serve as a USB-to-SPDIF converter for the Coaxial input of the HA-1 - gave the best results I've personally heard, for USB sources with the HA-1 DAC, but I've long since dedicated my HA-1 to using an Optical input from my flatscreen TV, to drive a pair of LCD-2 Rev 1. for late night TV viewing (or just for excellent audio TV viewing).
In this application, I'm not using the USB input and the HA-1's somewhat bright DAC section works very well with the shelved highs of my LCD-2 Rev.1 - not overlooking the awesome amp section of the HA-1.
So...
In my opinion, the Sonica DAC should be seen by HA-1 owners as a welcome upgrade - in terms of improving sound quality - in addition to all the other features it has. I think anyone who tries it with the HA-1 will decide to keep the Sonica DAC - even if they are already using Coaxial or Optical input vs. the USB input - and especially if they are using highly resolving, and treble-sensitive dynamic headphones like the Senn HD800/HD800s or the 600-Ohm Beyerdynamic DT880, for example. I fatigue when using them with the HA-1's DAC, even with Coaxial or Optical input, but not so when using the HA-1's amp section with the Sonica DAC.
Let me confess that although I spent a weekend listening to the Sonica DAC + HA-1, I don't run them together as a rule. (Again, I use the HA-1 by itself with optical input from the TV + LCD-2 Rev.1.) My Sonica DAC is at my recliner in the den, driving my (believe it or not) iBasso PB2 portable balanced amp, equipped with Sparkos Labs SS3602 discrete op-amps + dummy buffers, into the Oppo PM-1. THIS is my favorite combo, currently, for just enjoying music (primarily Tidal HiFi via the Sonica App, running on an Apple 6th Gen Touch, for long listening without fatigue, across multiple genres.
