> I want to learn more about what is meant by "logic" features
A basic quad matrix decoder provides only about 3dB channel separation
between certain channel pairs;
Left Front - Left Rear
Right Front - Right Rear
Left Front - Right Rear
Right Front - Left Rear
The channel separation is reasonably good only between the two front
channels and between the two rear channels. It is practically the same as
the sound carrier, LP, tape...
To enhance the channel separation subjectively, so called "logic decoders"
were developed. They use gain riding at all decoder outputs.
For example, if there is a higher level after the matrix decoding in the
Front Right channel, that channel is boosted slightly and (in some
decoders) all of the other three channels are damped down a bit. There are
certain time constants for the gain changes.
All four outputs have a similar gain riding system. The system is
the time the matrix output levels and does the gain riding dynamically
as the music changes. As a result, the listener subjectively hears a better
channel separation between all of the four channels than what a matrix
decoder as such can provide.
I'm not sure if you'd be happy to do the same with two channel stereo?
In order to make two channel stereo sound "wider", or to make an impression
that the sound is coming from two loudspeakers, you would ride the gain
L and R mixer faders along with the music.