Don't worry about the impedance, the 4ohm spec is just the minimum impedance per channel for the amp. Running an 8ohm speaker on each channel won't be a problem. It's power output will roughly be cut in half, making it what, 60-70 watts per channel? If so, the amp doesn't have nearly enough power to drive those speakers to full volume. Whether or not it has enough to get them loud enough for you, that will be up to you to decide by trying. Take care not to clip the amp too much.