There has been a fair bit of discussion about the setup of a HD621 with and without an Oppo 203/205 and the use of a Vanity card's, both the Oppo and the Vanity card have been sadly discontinued, there are some work-arounds that seem to work to some degree.

Those fortunate to have an Oppo 203/205 and want to use them in our systems for either video or audio throughput or Roon endpoint, there are some issues that have been raised, linear instead of switch-mode power supply, digital instead of analogue outs (what a Vanity card did), and the limitation of down-sampling restrictions as a Roon endpoint. Plus for those wanting a SACD player, these modifications can all be found at www.oppomod.com, they are reasonably priced and simple to install.

Hope this helps for those looking at getting the most out of their Oppo's and HD621.
Gerard.

Home Theater: LG 4K C7, HD621, G61RSL, Oppo 203, MS600, DSP3100 L & R, 2x3100's centers and 4xDSP3100's surrounds. 2x REL S3 SHO and 2x REL habitat1 subwoofers.
Music & TV: Sony 4k XBR 65", Oppo 203, HD621, G68D, C15, 588, M10, M20's, M33's, 4xDSP33's
MD600, 2xTwinStores.. 2xMS600, F80, Prime headphone and PSU.