@hog_tech - You cannot bi-amp with a single 2-channel amplifier, like the A21, regardless of how many speaker connections it has. 2 channel amplifiers that have A&B speaker connections share the 2 channels of amplification between the 4 speakers. The amplifier connects the 2 Left speaker cables and the 2 right speaker cables inside of the amplifier.
If you want to bi-amp, you need 4 channels of amplification.
You can bi-wire with a 2-channel amplifier that has 2 sets of speaker connectors. However, you can also bi-wire with one set of speaker connectors, running bi-wire cable that are 1 into 2 (one set of connectors on the amp side, 2 sets of connectors on the speaker side). Or you can stack 2 pair of speaker cables using spades, or spades and bananas, as Eric suggested.