No, that is not exactly what
@TLS Guy was saying but it does apply to old mono tracks being slapped on a disc or streamed as DD, DTS or PCM 2.0.
Two channel music with vocals can be up mixed quite nicely BUT the vocals will be steered to the Center Channel Speaker unless one applies Dolby Center Spread when using the Dolby Surround up mixer.
In the case of Onkyo receivers, one can use the Dolby Surround or DTS Neural:X/Virtual:X up mixers and use Onkyo’s own Vocal enhancement feature which can spread the vocals across the front stage to varying degrees. Dolby Center Spread is an ON or OFF affair that only works with the Dolby Surround up mixer.
There are exceptions to the rule and a PC or Mac configured to output multichannel PCM will behave a bit differently when two channel signals are output and up mixed.
Mono tracks disguised as Stereo can trip up the up mixers. They do for me anyway and I often just switch to the Mono sound mode in my Onkyo which outputs 1.1. The dialogue is nice and clear and a signal is sent to the subwoofer so there is a bit of rumble to the goings on and it doesn’t sound like it is being played from an old TV with a single, sad little speaker.
There are those mono 1.0 discs out there that aren’t up mixed well like certain 2.0 discs and streams that began life in mono. Dialogue can bleed out everywhere along with everything else.