350 hours on my DP-777 now, and the sound starts to stabilize, the tubed SPDIF input sounds best so far, the USB input is nowhere close to its own SPDIF or my Off-Ramp4 (with dual clock and battery options) connected to SPDIF. I bought a Macbook Pro and it's slightly better than my optimized PC, but without Off-Ramp4 the AMR has no magic with PC or Mac. I'll report back after 500 hours, but I doubt the USB will ever catch up.
For me, there are only two reasons to buy AMR DP-777: the tubed SPDIF input and the classic DAC. All the other options (HD Dac, filters, volume, USB) are good to have, and works above average Hi-Fi, but not stellar.
Jeffga, as much as I like the DP-777 I won't give it A+ if I am a Stereophile reviewer. The Grace M903 is less of a DAC and more of a headphone amp, and it does the headphone amp job extremely well, I have no problem giving it A+, but will probably move it to the headphone and accessory section, not the DAC section.