I feel it's the ultimate in flexibility! The only thing I feel I'm missing to get ANY tone would be a graphic eq on them both, but that's just getting silly now isn't it! Lol
John entwistle (I think) ran a guitar distortion for top, and just straight DI to a PA eq section to exact the bass end.
For me, the sansamp rpm is plenty fat enough anyway, as long as the blend is no more than half way!
I am however, one of these bass players that will never be happy without a 15" driver for the bass end!
I tried the guitar head and cab thing, but I much prefer the RBI into a sealed 10s cab