I'm not very familiar with Denon gear, but I would expect that your speakers have a higher power handling than your receiver can output.
The answer to this is as simple as grade 7 science! If you remember the experiment where you wrap copper wire around a nail, and then connect the other end of the wire to a battery, the end result is a magnetic Field generated to the nail. Amplifiers and loudspeakers work the same way, the current from the amplifier travels along a wire, and when it gets to the speaker, the current feeds the positive and negative poles of the magnet which determines the direction of the voice coil, which moves the drive unit in and out.
Having said this, and the above statement, you want to get as much current to your speakers as possible, to be able to drive them efficiently, if you go with single wire there will be more wasted power due to resistance, if you opt to bi-wire you will be able to get more power (current) to them, more current=more control=better sound
PS. in a bi-wire configuration you don't have to worry about impedance having 2 sets of wire connected to the amplifier because you aren't driving 2 sets of full range speakers, you are only driving HF and LF portions of one speaker, so no impedance drop because of this.
Happy Listening!