Desktop Integrated w/ USB.

Here's a shortlist of what I'm thinking:

-Nad D3020
-PS Audio Sprout
-Denon PMA50
-Musical Fidelity V90 AMP
-Maybe something from TEAC?

I really like my 3020D (V1)

I can recommend them as musical and capable. They make slightly larger units as well.

@erik_squires  

Thank you.  That's what I'm leaning towards at the moment.

In terms of Class D, these are some intriguing amps. The design apparently comes from Hypex, but based on the literature, it is closer to the old NAD or Carver type of design, with floating voltage rails driven Class D, but a small Class A amp actually driving the speakers.

Yamaha's EEEnginge and Nuforce seem to be doing similar things.

Best,
E

Just went with a used NuForce DDA120.

The DDA120 should be here tomorrow.

I should mention that it'll be replacing a pair of AudioEngine A2+.  I've really enjoyed the A2s, but due to their size and power, they definitely have their limitations.

Going to try the DDA120 with my NHT Verve speakers first, and then bring in the Tektons if needed.  The great thing about the NHTs is that they'll fit on my desk, and look much cooler than the Tektons.

More updates to follow..

I've got the PMA-50 on my desk.  I can't say it's amazing or anything as I have it pushing some cheap 5" Klipsch speakers I got on Black Friday a few years back, without a sub.  It's not great in terms of lows, but sounds decent for a lower priced setup, and fits well on my small desktop.  I bet it would be pretty nice with some better speakers. Overall, I like it and think it's nice for when I don't want to fire up my bigger system.

@irrenarzt

I'm using a Denon PMA1600ne in my main system, and absolutely love it.  I was seriously considering the newer PMA-60, but the NuForce was easier on my bank account.