The JRetro could be used without a rackmount preamp, but it wouldn't push the power amp to full power...I'd get the RBI, then the Retro, so I had a preamp before and after the onboard...
unless you need the DI out on the sansamp, then the J Retro should be more than enough. but most preamps and amp heads have a DI out, so you prolly wouldnt need the Sansamp. also, if you really need a good tubey overdriven sound to your bass, then the Sansamp might be worth holding onto.
