It’s strongly recommended to compare different receivers if you want to choose the best one: Pioneer VSX-LX503 vs Pioneer VSX-531.
The number of channels for receivers is different - 9.2 versus 5.1, respectively, for devices. In terms of power, there are differences, the VSX-LX503 has such a ratio W/Ohm - 120/8, 230/6, while the VSX-531 has a power of 80/8, 140/6. A common feature for devices is the same total harmonic distortion - 0.08%.
The manufacturer installed different DACs, the VSX-LX503 received the model AK4458 384 KHz/32-bit, but the VSX-531 is equipped with 192 KHz/24-bit. The Bi-amping function is implemented only in the Pioneer VSX-LX503. Both Pioneer VSX-LX503 and Pioneer VSX-531 can transmit an audio signal directly to the amplifier and bypasses any DSP processing. Each of the receivers has a Bluetooth connector. The VSX-LX503 has access to the Spotify service. The quality of 4K/60Hz signal remains unchanged when transmitting from a source to a TV or projector via HDMI for both receivers. Signaling over HDMI in standby mode can provide the VSX-LX503 and the VSX-531. Video scaling is only possible with the VSX-LX503. Operation with the Dolby Vision is only possible with the VSX-LX503.
The number of HDMI inputs/outputs varies depending on the receiver, the VSX-LX503 has 7/2, and the VSX-531 has 4/1. HDMI Audio Return Channel is implemented in both devices. HDMI eARC is not supported by the VSX-LX503 and the VSX-531. When comparing receivers, it becomes clear that each of the rivals can work with HDMI CEC. VSX-LX503 and VSX-531 support the standard HDCP 2.2. In the presence of a built-in phono stage for connecting a vinyl player only at Pioneer VSX-LX503. There is an ECO mode in VSX-531. The Pioneer VSX-LX503 can be properly configured using the setup assistant.
A Dolby Atmos multichannel audio format is available only in the VSX-LX503. Only in the VSX-LX503 realized a DTS:X surround technology.