adding second set of speakers

Yeah okay I did silly stuff like this when I was a kid too. Stack em, more louder, cool. 

But I can guarantee that is all you will get more of, volume.

One trick you might try, that might actually be not just louder but better: Pick whichever pair you like best, set them up as best you can for imaging. The other pair, open up and disconnect the tweeter. Then place these down on the floor facing a wall in a corner. Since these are 2-way speakers even with the tweeter out the woofers go quite high so use a pillow or blanket to absorb as much of that as you can. You are basically, in other words, using them as subwoofers.

If you can set them up so you can't hear anything from them but low bass then you should be able to find locations that get you quite a bit more extension and improved imaging at the same time.  

well now, that is interesting and i would have never thought of doing the disconnect the tweeter thing.... I do have two excellent corners on either side of my listening position...

i fully agree with millercarbon here--adding more speakers, especially of a different brand, will give you more decibels, but will very likely sound worse--you're probably better off with one well-placed set

@millercarbon
  well, i went and done it. i wyred up the JBL’s and pointed them in corners directly beside my listening position as my couch is at the far wall with main monitors directly in front of me. now I have set the high pass sub woofer to 80Hz so the 4 monitors are getting everything 80Hz and up. with the JBL’s up about one-third, the soundstage is pretty wide. I am liking this. Now, I did not disconnect the tweeters. Do you feel this will be an added benefit? You mention using some pillows to control the sound... please elaborate. One thing I will try is wiring the JBL’s to the full range inputs and see what that sounds like...

Just curious, how do you like the Model One's?  I've had mine for almost two years now and feel they sound pretty darn good for the $ but haven't seen too many (If any) threads about these sleepers