IA + DAC: I would just get a nice AVR like the Denon AVR-3311CI
The Denon's DAC will be every bit as great as any DAC you will buy.
And the sound quality of the Denon AVR will sound as great as any Integrated amp you will buy.
Speakers: I would get a pair of NHT Absolute Zero
. Add a 10" or 12" sub as your office space will allow.NHT Measurements
"The Absolute Zero's listening-window response (a five-point average of axial and +/-15-degree horizontal and vertical responses) measures +0.94/-0.82 decibels from 200 hertz to 10 kilohertz."
Can't beat that accuracy.