Don't both speakers use the same mid and tweeter? So, other than allowing you to position the "woofers" in the 2.3's from the Mid/Tweeter in the 2.1's, what purpose would this serve? Wouldn't be easier to just use a sub, or a pair of subs, with the 2.1's and set the crossover a little higher? I wouldn't recommend setting it too high or you'll risk being able to localize the bass.