Can I control 3 rows of 2 lights/row using 3, 3-way switches in two locations connected by a single 3-wire cable between switches?

Absolutely not. You'll need a 3-wire for each set of 3-way switches.

One Bank of switches will need a constant hot and ground. The other Bank will need the 3 sets of lights run to it(hot, neutral and ground. Between the 2 switch banks, you will need 2 travelers for each switch. 2 Blue, 2 Brown, and 2 purple for example, and a ground.

Just remembered, you could do that with 6 Insteon 2477D's. Could be pricey. But Doable.