No need to buy any more kits. You have plenty of options to go with your ego battery.
I didn't like the ego-t tanks either. I use the dual coil tank (DCT) + cartos with my ego batteries. Personally, I prefer the 1.7 single coil cartos in the tank (rather than the dual coil cartos that come with it). Pre-punched cartos can be bought from many vendors - Crystal Clear Vaping, Hoosier, etc..
I prefer cartos much more than atties (I like low maintenence), and would recommend giving some a shot. I think I'd recommend just picking up a couple of the Boge LR (2.0 ohm) or the Smoktech single coil (1.7 ohm) before investing in a tank just to see if you'll like cartos.
If you like them, then try out one of the small (3.5ml) tanks - they work great for me, and make cartos even more low maintenence.
If you're interested, I can give links to specific things that I mentioned.
Err how's he gonna get a 7.7 watt vape from a 3.4 volt device and a 3 ohm cartomizer?
I don't know how that watt/volt/ohm math works, but the DCs that come with those tanks are two 3ohm coils, and equal a total of 1.5ohm.