Your Marantz is a good AVR that has the latest HMDI 1.4 and decoder capabilities - it also has a full set of pre-outs. Absolutely no reason to chnage this receiver. Get the B&W 683's over the 684's right now. The 683 is a much better speaker and you won;t regret it. If you feel your Marntz can't get the job done, then as others have pointed out, get a 2 channel power amp and use those L/R Pre-Outs on the Marantz. There are many fine models at 100-150 wpc under a $1000. Some brands were already mentioned to you. This will certainly be less than buying a new receiver. And a seperate 2 channel power amp will make those 683's sound better tghan the most expensive AVR ever could. Finally, whether a speaker is 3 way or 2 way, has no bearing on the type of pre-amp use. You'll be fine.
