AVR Surround Modes
Dolby Digital or DTS 5.1 are the only discrete surround modes available in the AVR 146 (that is, all 5.1 channels are discrete), but how enveloping they are is entirely program-dependentsome material has lots of stuff in the surround channels, while other content doesn't. The other modes will synthesize a surround soundfield, so they might actually be more enveloping in general, though possibly not as true to the content creator's intent. The only way to be sure of which one you like the best is to try them all with different program material.
Interestingly, this AVR has two HDMI inputs and one output, but they perform HDMI video switching onlythey do not process the data in any way, and they do not pass any audio data in the HDMI bitstream. So if your source device is connected via HDMI, you must also separately connect its audio outputcoax or optical digital or 5.1-channel analogto the receiver. The coax and optical connections will send only Dolby Digital or DTS, which is fine in your case. If you have a Blu-ray player, use the multichannel analog connection and have the player decode the audio, which will give you the benefit of Dolby TrueHD and DTS-HD lossless audio.
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