@doraymon: I have both the T/zero and the T/5i, and would have to recommend the T/5i. I bought it precisely because the Tzero, while performing well for its size, just doesn’t go low enough to really satisfy with the Omegas. It’s a 6.5" driver and you can’t fight the laws of physics. The T/5i doesn’t cost all that much more but ensures that you won’t find yourself second guessing your decision should the T/zero not fit the bill.
The damping factor issue is a real one with the Omegas, which I find very susceptible to over damping. I have two First Watt amps - the F2-J, with a damping factor of about 0.5, and the SIT-3, with a damping factor of about 30. Even though 30 is not a huge number by any measure, you can still tell the difference in bass performance. Notwithstanding the other differences between those two circuits, in general I think the lower the damping factor, the better with the Omegas!