While the achievement is easy in theory... you still need ALL four instruments connected to YOUR console to get it. Why you ask?
This game does NOT feature Xbox LIVE multiplayer.
For compatible instruments that you can use with this game, look no further than the RockBand.com website:http://www.rockband.com/compatibility
The following games include bundled instruments that are compatible:Rock BandRock Band 2The Beatles: Rock BandGuitar Hero IIGuitar Hero III: Legends of RockGuitar Hero: AerosmithGuitar Hero: World TourGuitar Hero 5Band HeroGuitar Hero: Warriors of RockLips
Below is a list of instruments that are believed to be fully compatible with Rock Band and All Track Packs (including AC/DC Live: Rock Band Track Pack).NOTE:
You will need to have 2-3 AA batteries for each wireless instrument, depending on the instruments used (6-8 AA batteries total). Some instruments in the list below will require 3 AA batteries!Guitar/Bass
(you will need any 2 of these; most are wireless unless noted):
Rock Band 2 Fender Stratocaster
Rock Band Fender Stratocaster (wired)
Mad Catz Fender Telecaster
Mad Catz Fender Precision Bass
The Beatles: Rock Band Hofner Bass
The Beatles: Rock Band Gretsch Duo-Jet
The Beatles: Rock Band RickenBacker 325
Guitar Hero: Warriors of Rock guitar
Guitar Hero 5 guitar
Band Hero guitar
Guitar Hero: World Tour guitar
Guitar Hero III: Legends of Rock Gibson Les Paul
Guitar Hero II Gibson X-Plorer (wired)Drums
(you'll need 1 from this list; most are wireless unless noted):
Rock Band 2 drums
Rock Band drums (wired)
The Beatles: Rock Band Ludwig drums
Guitar Hero: Warriors of Rock drums
Guitar Hero: World Tour drums
Band Hero drums
Rock Revolution drums
ION drums (wired)
MadCatz Rock Band 3 Midi PRO-Adapter for Xbox 360 in "D" mode setting (wired)Microphones
(you'll need 1 from this list; most are wired unless noted):
Any USB microphone*
Rock Band 2 microphone*
Rock Band microphone*
The Beatles: Rock Band microphone*
Guitar Hero: World Tour microphone*
Band Hero microphone*
Xbox 360 Wireless Microphone (bundled with Lips)*Xbox 360 Rock Band M.I.C. (Microphone with Integrated Controller)
* A standard Xbox 360 controller is also required to play vocals
, unless you are using the wired Xbox 360 Rock Band M.I.C.
Assuming that you have 2 guitar controllers (guitar/bass), drums, and microphone with standard Xbox 360 controller (vocals)...
Connect all controllers, including the microphone.
The instrument you prefer to play does NOT matter as you will not even need to play a song.
You can sign-in extra Gamertags as well and they too will also get the achievement.
From the main menu, choose:
MULTIPLAYER -> BAND QUICKPLAY
Press the green fret button on both guitar controllers (guitar/bass).
(OR tap the green pad) on the drums.
on the standard Xbox 360 controller (vocals).
(guitar: green fret button/drums: green pad) on the controller that is the band "leader" (noted above the instrument icon).
Achievement unlocks at the setlist screen.
Feel free to leave the stage because you were only ABOUT TO ROCK. In other words, disconnect all controllers, go for a different achievement, play a different game... whatever you want. You're done.
And by the way... tell the crowd that you are going solo from this point on as the rest of the achievements in this game do NOT require a full band. Good luck!