Hi Wil5560,
let's clear some things.
When we are playing with our left hand with a style, we "control" several (midi) channels.
the bass channel,two chord channels,pad channel,two phrase channels and the muptipad channels.
So when we use the record function to create a midi song by playing with a style,at least 7 channels(instruments) are played just by our left hand.
Now,let's say that we want to play along with that midi.
We should mute those 7 channels.Right?
If we play with a style(while the midi is playing along we press the start button of the style part) the style will follow the chords of the midi,not the chords you are playing.
Not a good idea for practicing that way our left hand.
Maybe there is a way with midi orders and midi cables etc that can be done but better leave that option aside.
You could use a way that mentioned above to practice the left hand.
a) choose a voice,watch the chords the midi is displaying and hit them at the right timing while timing is playing.
The volume of the voice should be loud enough so you can hear when you are making a mistake.
b) Practice your left hand by playing just with a style.There is no need to be a melody line to practice.
You know the chords,hit them at the right timing.
There is no need to be a robot to find the exact millisecond.We don't play like robots, neither we will sound perfect if we play that way anyway.
c) Practice your left hand without a style or a midi and a rhythm.
Just press the correct chords at the correct timing.
When you feel ok,you could use the metronome to perfect your timing or use a style and mute all channels except from the rhy1 or rh2 channel.
When you feel that you are playing ok, add a melody with your right hand at your tempo at first.
Keep in mind that even if there would be a way to play the chords as you wish with a midi, you wouldn't practice your left hand properly to play an arranger keyboard with styles.
You must also practice your left hand to leave the keybed,push a button and then play the next chord.
Same with the right hand.Change the voices and keep playing.
Unless you don't want to learn to play with styles just with midis, but in that case there is no need for your left hand to learn to play "chords".