So I came up with Aurora 9 bar. It's a bare essential version of Aurora 9x18. In fact the circuit is almost exactly the same (with a lot less number of LEDs of course). Even the firmware is essentially the same. So it has the same super smooth color fades as Aurora 9x18.
Step 1: Concept & Circuit
Aurora 9 bar's circuit operates in the same exact way Aurora 9x18's does. Same PWM theme, same refresh rate, etc. Please refer to my Aurora 9x18 Instructable for the details.
Aurora 9 bar took one LED out from each of Aurora 9x18's 9 circles. Only difference in the circuit is that it uses BJTs instead of MOSFETs for the high-side switch (to save cost). Because there are only 9 LEDs total, the current requirement for the bus controllers is much lower.
Everything else is the same. So if you somehow manage to hook up more LEDs to Aurora 9 bar, it will look like Aurora 9x18.