I went with what I had as I couldn't get an adapter with the amperage I was looking for - four tubes (two cathode kits) on a 9volt 3amp adapter works fine. The light is pretty similar to a night with a full moon.
Splicing the two kits into one didn't pose much of a problem. I got a kit that consists of two white plastic parts that link into each other, which holds two male and two female connectors - the whole unit locks the wires into place. I stripped the ends of the two red wires from the kit and twisted them together, then put them into one of the connectors - it was then crimped, and soldered. Soldering isn't necessary, but I'm told it helps. This was also done with the two black wires from the kit, as well as the two wires from the 9volt adapter.
The whole set was then connected together - the red wires from the cathodes goes into the black wire with the broken line on the adapter, and the black wire goes into the black wire. I've placed the inverters, the red/black wires, and the adapter connection, inside a 'click clack' lunch container - this container has a rubber seal, as well as handles to lock the lid into place. I've cut a hole on the lip of the container and the lid so that the wires can all come out - they're pretty snug, though I will be sealing it with silicone. The wires that come out are the white one from the cathodes, and the black ones from the adapter.
So far I've only tested it out above the tank for 30 minutes as I'm yet to install it in the canopy. Unfortunately the nocturnal fish (plecos and synos) didn't venture out during this time, though the cichlids were very active. I may get some UV tubes at some point and see if there's a better response from the nocturnal fish.
The inverters inside the container didn't warm up at all during this time, though I was left wondering why I had an adapter converting mains AC power into DC, then an inverter converter DC back into AC - there's loses of power at both stages so it's pretty inefficient. The resulting brightness is at the right level for what I've got however, so I can't complain - if I do the project again though, it's something I'll be considering.