Difference between the Tech 21 sansamp RBI,RPM, & PSA 1.1

[Linehand 101]

HELLO-
I OWN AMPEG/KETTNER TUBE AMPS. LOOKING TO PURCHASE A BACK-UP PRE AMP, WHICH IS THE SANSAMP. FROM ALL THE INFORMATION i HAVE GATHERED, i WAS WONDERING IF ANYONE HAS A GOOD UNDERSTANDING OF THE DIFFERENCE BETWEEN THESE, AND WHAT ARE YOU GAINING BY LINKING THEM TOGETHER. (EX.-LOOPING A RBI AND A PSA 1.1) ANY FEEDBACK WOULD BE GREATLY APPRECIATED!

[Kenner]

I just use my Sansamp DI as my back up to my GK RB700/112. That way, if the amp dies, I still have signal to the FOH.

[Kenner]

The sansamp gives me a mountain of tone

[Linehand 101]

WHICH SANSAMP DO YOU OWN?

[Kenner]

The BassDriver DI