HDMI 2.0 (4K/60Hz pass-through), Optical, Coaxial, and 3.5mm/RCA outputs.
Look for kits that offer a "5.1/7.1 switch." This allows the decoder to intelligently distribute sound even if your source material only supports 5.1. 7.1 dts dolby digital decoder kit
Buying tips
You have a beautiful collection of vintage stereo power amps (e.g., old Adcom, Rotel, or Hafler). You want surround sound without buying a modern plastic receiver. Use one decoder kit to feed signal into your four vintage stereo amps. HDMI 2
Setting up your is straightforward if you follow this wiring diagram (in principle): HDMI 2.0 (4K/60Hz pass-through)