The only way to get this achievement is to be playing in a 4-player band (guitar, drums, vocals, and bass), successfully complete a band moment, and then try to have each player up to a 4x multiplier AND at least a half bar of star power, then after (or before, I don't believe it matters) the band moment, all 4 members deploy star power.
Sounds really complicated, but it's actually a bit more simple than that. Not much, but a bit.
Basically, set up your band with all four unique instruments being used and select your respective difficulties.
Then, simply play a song and hold on to your star power until the band moment comes. All four activate, pop.
I don't recall which song I ended up getting this achievement on, but what I do know is if you're having problems (or your bandmates are) keeping a 4x multiplier, drop down in difficulty.