I don't think it makes any sense duplicating your keyboard...maybe a similar board...as an example a Roland G70 and a BK9...or a PSR s950 and a Tyros2..

If you own a laptop, you have the best back up, no matter what fails for you..

As for sound systems...I have never had a single failure with my Cubes in 29 years, I only carry two for stereo..

Keyboard wise, the MS would not boot one night on stage and I didn't have a keypad to move the request for booting..

The band sound system had a tweeter blow out and was very evident..Good thing we are always in stereo (two units)..

Keyboard wise ..I always had more than one keyboard...not because I needed a backup....just that I wanted more than one..

Now that we all have smart phones..the show can always go on..I have 32 gigs of MP3's on board my phone and can go to you tube for any request....and voice recognition works great..I say the request and play the song..