My comments refer to the Denon, my suggestion is on the basis of providing you with high quality DVD and CD capability that you referred to in your original post.

The Denon HDMI would need to go into the HD621 for DVD and CD.

The Oppo 203 has multiple output options, listed below:

Rear Panel Connectors

1. Gigabit Ethernet LAN Port
2. HDMI Output (Main)
3. HDMI Output (Audio Only)
4. HDMI Input
5. Optical Digital Audio Output
6. Coaxial Digital Audio Output
7. USB 3.0 Input
8. USB 3.0 Input
9. RS-232C Serial Control Port
10. Trigger Output
11. Trigger Input
12. IR (Infrared) Sensor
13. 7.1CH / 5.1CH / Stereo Analog
Audio Output
14. AC Power Inlet
The AC power inlet is the IEC60-320 C14 type. Only the included AC power cord or an approved power cord
with an IEC60-320 C14 type plug should be used.

The Oppo is an excellent Bluray and 4K player. CD playback is okay but not as smooth as a Meridian 800.

Hope this helps.

Cinema: DSP750 x3, DSP3300 x 4, DSW.2 x 3, Trinnov A32, 271, Oppo 203, Toshiba HD-DVD, SKY Puck, Sony XW7000 PJ, Screen Research AT, Kaleidescape 4K 30TB
Lounge: 861v8, 808v6, UHD722, DSP8000SEPP, DSP7200HCSE, DSP3300, DSW x 2, 504, C15, Sony UBP-X800, SKY Puck
Bedroom: DSP5200SEHC, G65, UHD722, G08, DSW, M6, C15, 210, SKY Puck
Spare: 818v3