I biamp my Linn speakers using horizontal biamping, which is what Linn recommend. For Vandersteen, I would give great respect to what Mr. Vandersteen says, as noted in the post/link above.
For your application try both and see which you like. There are (or should be) some differences.
Although you have identical amps, horizontal biamping allows you to try some interesting things by using different amps. For example, you could put a more powerful amp on the bottom for greater woofer control. Or you could try mixing tubes and solid state for top and bottom. Just make sure the gain is the same if you experiment in the future using different amps.
For your application try both and see which you like. There are (or should be) some differences.
Although you have identical amps, horizontal biamping allows you to try some interesting things by using different amps. For example, you could put a more powerful amp on the bottom for greater woofer control. Or you could try mixing tubes and solid state for top and bottom. Just make sure the gain is the same if you experiment in the future using different amps.