Cam, I don't understand what you mean by the right tweeter being closer? Why isn't the entire M3 closer? Assuming you mean that the right M3 is closer to your listening position than the left M3, I recommend you try lowering the volume of the right, increasing the volume of the left or a bit of both.

As for the bass, there is plenty in the M3 but not like the Monitor 9. Perhaps too, you are encountering a bass null at your listening position. A sub, properly placed, could fix that.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated