Quick impressions, yes.
Both are built extremely well. The Audio-GD C-2 is a utilitarian tank--it's huge and is built for function over everything else. The Garage1217 Project Polaris is gorgeous--especially with the acrylic--and has a much smaller footprint.
In terms of sheer clarity and detail, the Audio-GD is slightly better. I am able to distinguish instruments a little better with it overall. It isn't night and day, it's more like 12:00pm vs. 1:00pm.
Like the Polaris, you can customize the warmth of the C-2 via jumpers. Essentially, you can make treble roll off at different points to smooth out harsher recordings or headphones. The C-2 requires you to take out the power cable, remove a bunch of screws, and change the jumpers. Once you're set, you're kinda set. The Polaris is super quick and easy to change within seconds.
In terms of sheer versatility, the Polaris certainly wins. The only way it could be easier is if there were switches instead of jumpers, but the jumpers are super quick to change.
If you're looking for a step up from the Project Polaris and are okay with paying twice as much and can handle a footprint of 14.25" x 9.5" x 3.25", the C-2 is a little better. If you want versatility, value, and don't want something to dominate your desk, the Project Polaris is excellent.
I've already decided to keep the C-2 for home (unless I sell it for the NFB-1AMP and go fully balanced). For work, I'm trying to decide between the Project Polaris with a TBD smaller form DAC or an Audio-GD NFB-15, which I don't have yet. I had the C-2 at work for a day and people kept getting distracted by its size, so it went home.
