Thanks for the forum tip and your advice--is there a way to tell by looking at the back of the receiver what gauge wire it can handle?
You can start by assuming the speaker wire commonly used when that receiver was new, was nowhere as large as what people use now. At the time, just about everyone sold or gave 18 ga wire with most of the equipment from mainstream equipment. If the wire needed to be longer than about 30', it was usually 16 ga, but NOBODY was using 12 ga for anything other than high power amplifiers until companies like Munster Cable came along. If your speakers are less than 40' from your receiver, 12 ga is really overkill. If you have a wire stripper that has holes for different gauges or wire, use the 14 ga hole- the loss of a few strands of wire won't make any difference in the sound.
FYI- that receiver WAS NOT made for speakers like the Vandersteens and if you look at the area around the speaker terminals, you'll see that it clearly states 8 Ohm speakers are to be used. Also, the speaker selector switch puts A in series with B, which keeps the amplifier from overheating when low impedance speakers are used. If you like your music loud, either put a fan on the receiver to cool it or use a different amplifier. Fortunately, your receiver has preamp output and power amp input jacks.