How to connect my Tascam rw900sl CD Recorder to a new 2-channel stereo receiver (onkyo 8270) without tape in/out RCA jacks and

For playback you can connect it to any input except phono. This included the digital inputs. You can try both analog and digital and decide if one sounds better than the other.
You may be able use the zone 2 audio output for recording. Some receivers won't send audio from sources that are connected via HDMI or SPDIF through the zone 2 analog audio output. Any sources with digital outputs can connect directly to the digital inputs on the Tascam.