Since you're discussing parallel and in series, what would be better when hooking up a pair of speakers on say the left channel and a pair on the right channel?
This depends on the impedance of both the amp output and the speakers,
If you have say, two 4 ohm speakers, and an amp with 8 ohm output, you want them in series
If however reversed, IE the amp is 4 ohm output and the speakers are 8 each, put them in parallel will make the impedance half. This is different than voltage.
If you don't know, try them either way. It might be say, if the speakers are poorly matched, that using all 4 hurts the end result rather than two
Also on speakers polarity is important, because they combination can produce interferance waves and deteriorate the sound. "In general" you want all positives matched on all channels.
