I measured the current draw of the Minibrute at right around 300mA @ 12V (powering it from a bench top power supply w/ current load readout).
From the design of the power supply it looks like you could use anything from 9V to 16V without trouble.
There's a fuse, zener diode, and crowbar protection circuit at the input.
After that there's DC-DC stepdown IC that should be fine with an input from 9V up to 16V (it's a switching regulator so heat is not an issue).
Preferably stick to 12V, but I wouldn't expect any issues with 9V or 16V (1A minimum), but it's your synth and warranty!
The power supply is actually very robust and redundant, as it's laid out clean and all the analog and digital supply votlages are isolated. This is miles beyond to the consumer-oriented construction of the Novation Bass Station 2.