I have very effective and natural-sounding mini-setup.
Up to now all bass amps I have tested dissatisfied me because they always color the sound very much, and I don't have the feeling that I get an "acoustic" sound from my Mahogany Fretless.
Since I know more and more double bass players who play through active speakers instead of a bass amp, I tested it myself.
Now I have a QSC K8. Really great sounding, very smooth, not too much mids (like the new Yamahas...). Of course the K10 sounds even fuller, but I like very compact setups, and for small venues the K8 absolutely suffices. And I additionally have a very good PA box when I need one.
Preamp is also crucial - here I found (like many others already did) that the Fdeck HPF-Pre (mine is the Series 2) is THE device to go. MUCH better than the Fishman Platinum Pro I also own which totally colors the sound in a "wooly" way and doesn't allow for even distribution of loudness/punch/fatness across the bass` frequency spectrum. The Fdeck does this very well and easily. Speak about Plug and Play!
Now with just these 2 devices the tone is really beautiful and "acoustic", but sometimes has too little "punch". Because turning up mids does a disservice to the sound, I have a "Okko Coca Comp" (German handmade) compressor pedal in the signal chain between the Fdeck and the speaker which rather ingeniously adds punch without reducing the dynamics so much or adding artificial sounding color. This is handy when I play with drums, for instance.