I just added bass to my guitar playing, so I bow to your experience. Neil Young is famous for his rig. He uses a tweed Deluxe amp - 20 watts - mic'd into his own P.A. on stage, which feeds the house P.A. So instead of using massive tube amps to get tone+volume or SS and sacrifice tube tone, why not use a small tube amp tuned to bass freq -> mic -> SS power amp -> speaker cab. It's similar to using a preamp but it lets you choose the amp/speaker combo and it gets real tube tone. It also deals with the "I'm not loud enough for my band" thing. Just a thought.