The center channel needs to be either the exact same speaker as the right/left (your setup) or a perfectly "matched" speaker. I use B&W Nautilus 804s for my left/right and an HTM-1 for the center. The HTM-1 is essentially an N804 on its side, having exactly the same tweeter, mid-range driver and both bass drivers (while horizontal centers are not the best, the HTM-1 does have the proper vertical arrangement for the tweeter and midrange, with both bass drivers on either side). For your setup I would keep the 801III, as you have the same front three speakers. If you want to upgrade the best way would be to change all three front speakers.