Did you test 800 SPDIF bs Oppo HDMI + HD621? Or what precise combination of devices and interfaces?
Well, I compared 800 via SPDIF versus BDP83 via both SPDIF and HDMI, the latter obviously using HD621. I did these comparisons with both the 861v4 and 861v6. When playing CD, with the v4, I found the performance of both players to be very close (I could not reliably differentiate the Oppo SPDIF vs. HDMI) although ultimatley preferred the 800. When playing CD, with the v6, the superiority of 800 became somewhat more apparent.
These comparisons do not, however, tell much about the 'levelling' effect of the HD621. One would have to compare mulitple players outputting over HDMI, which I have not done.