Since I am guessing that speakers playing at around 80 db in the ofice is out of the question and you will be doing headphone listening...The Benchmark and Grace DACs are probably good choices. The New Headroom products are also options.

You could also look at the Channel Islands DAC and Headphone amp as a set. I think Musical Fidelity could also hook you up as well with a DAC and X-Cans headphone amp.

M-Audio also makes what they call their Super DAC (24/96 AKM converters) that is around $250 and sounds decent. It is not up to the BenchMark or Grace standards.

Good headphones can reveal great detail so choose converters based on how they sound to you.

I have not done that. If price is an issue I know of number of friends who bought the PreSonus Headphone amp at $99 and were happy with it. Presonus HP4