Just checked the manual, and I can see what's happening...
Here's what it says on P.15:
"Be careful when using two pairs of front speakers (A+B) at the same time, since use of speakers with an impedance of 12 to 16 ohms"
This appears to be an incomplete sentence to me. Still, if you use two pairs of identical 12 ohms speakers at the same time, the amplifier will see it as one pair of 6 ohms speaker from the impedance/loading stand point. If you connect two pairs of 6 ohms speakers to the front and power them simultaneously, each channel/amplifier will see a 3 ohm load, and that is definitely not good for your 1705. Another thing that puzzles me is that on another page (34/35 I think), it talks about a speaker selection button that allows you to select A, or B, but no mentioning of A+B. So how do you select A+B anyway?
Hope this help, I just don't want you to cause any damage to your new receiver because part of the manual was poorly written.