In this multichannel mode, I would prefer to set the output route of each pattern-channel, not of each instrument.
This is a bit tricky for one reason -- when you are writing a tune from ground
up, that wouldn't make much difference, if you route from the channel or
the instrument. Yet if you want to mess around with an oldie that may be
a bit of a problem, because the instruments are all over the channels
there.
So you might end up with strings or drums changing speakers from
pattern to pattern if you limit yourself to channel routing only.