I use a Fdeck HPF (http://www.talkbass.com/forum/f15/fdecks-hpf-865291/) in front of my DB and my Ubass. It makes everything sound better than all the rest I've tried. I have tried LOADS of stuff and the HPF beats them all, for me. It does not do gain or a DI, but a DI box is cheap. People talk all sorts of stuff about one DI being better than another. Once your signal is buffered properly then a cheap and cheerful DI will do the job nicely. Of course, if you are recording at SARM West and Donald Fagan is employing you, then there are certainly other options.