It makes sense comparing Onkyo TX-SR343 vs Pioneer Elite SC-99 because they both are able to give some premium features.
A significant difference between the receivers in the number of channels, Onkyo TX-SR343 has 5.1 versus 9.2 for Pioneer Elite SC-99. Regarding power, then TX-SR343 has such a W/Ohm ratio - 100/6 when Elite SC-99 has a power of 140/8, 200/6, 255/4. The THD is the same and is 0.08%.
Characteristics of digital to analog converter (DAC) are different, TI Burr-Brown 192 KHz/24-bit for TX-SR343 and ESS SABRE 192 KHz/32-bit for the Elite SC-99. Only the Elite SC-99 supports Bi-amping feature. The Pioneer Elite SC-99 can transmit an audio signal directly to the amplifier and bypasses any DSP processing. Rivals from our review have Bluetooth support. Only the Elite SC-99 supports Spotify.
Only the Pioneer Elite SC-99 has support for High dynamic range (HDR). Compared AV receivers retain the quality of 4K/60Hz signal when transmitting from a source to a TV or projector. HDMI signal transmission in standby mode is implemented in each of the devices. The Elite SC-99 can scale the input HDMI signal, unlike the TX-SR343. The HDR standard - Dolby Vision is not supported by these receivers.
The Onkyo TX-SR343 has 4/1 HDMI inputs/outputs versus 8/3 HDMI connectors of the Pioneer Elite SC-99. The HDMI Audio Return Channel (ARC) feature supports both devices. Unfortunately, HDMI eARC is not available on monitored devices. Of the two receivers in our comparison, HDMI CEC is present in only the TX-SR343. Both models support the standard HDCP 2.2. The Elite SC-99 has a built-in phono stage for connecting a vinyl player. A voice control is not available. An ECO mode is only available for the Elite SC-99. The setup assistant will help you configure Pioneer Elite SC-99.
Only the Elite SC-99 has a Dolby Atmos multichannel audio format support. The receivers do not support the surround sound technology DTS:X.