It makes sense comparing Pioneer VSX-LX303 vs Marantz NR1509 because they both are able to give some premium features.
A significant difference between the receivers in the number of channels, Pioneer VSX-LX303 has 9.2 versus 5.2 for Marantz NR1509. Regarding power, then VSX-LX303 has such a W/Ohm ratio - 100/8, 200/6 when NR1509 has a power of 50/8, 60/6. The THD is the same and is 0.08%.
Characteristics of digital to analog converter (DAC) are different, AK4458 384 KHz/32-bit for VSX-LX303 and 192 KHz/24-bit for the NR1509. Only the VSX-LX303 supports Bi-amping feature. Each of the AV receivers can transmit an audio signal directly to the amplifier and bypasses any DSP processing.
WI-FI modules have the same characteristics: 2.4/5GHz. Rivals from our review have Bluetooth support. The Pioneer VSX-LX303 has support for AirPlay, and its competitor in our comparison - AirPlay, AirPlay 2. Spotify can be used on each receiver. The VSX-LX303 can work with the audio stream from Deezer, TIDAL, Pandora, TuneIn Radio, and the NR1509 can receive a content from Deezer, Pandora, TuneIn Radio. 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 VSX-LX303 can scale the input HDMI signal, unlike the NR1509. The HDR standard - Dolby Vision is supported by these receivers.
The Pioneer VSX-LX303 has 7/2 HDMI inputs/outputs versus 7/1 HDMI connectors of the Marantz NR1509. The HDMI Audio Return Channel (ARC) feature supports both devices. Unfortunately, HDMI eARC is not available on monitored devices. The Consumer Electronics Control (CEC) feature is present in most modern AV receivers and the models in our comparison are no exception. Both models support the standard HDCP 2.2. These compared receivers have a built-in phono stage for connecting a vinyl player. The VSX-LX303 supports voice control via Google Assistant, and the NR1509 - Amazon Alexa, Google Assistant, Siri, Josh.AI. An ECO mode is only available for the NR1509. Both VSX-LX303 and NR1509 can be configured using the Setup assistant.
Only the VSX-LX303 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the VSX-LX303.