As much as I love source audio stuff and how it sounds, I think it's probably entirely valid to say that
1) Using an expression with the Manta, in whatever form, takes up a lot more space than just a wah alone.
2) Many expression pedals -feel- different from the usual wah pedal format
3) It might be pretty difficult to cop a particular wah tone from the Manta + expression combination, especially with the whole too-many-knobs thing
So yeah, if those three points weigh heavier than the flexibility and power of the manta, then clearly this option isn't suitable. That said, I'd say that for a traditional player, expression + BEF might be more useful than expression + manta, since you can stick in a traditional expression pedal, and wouldn't need the built-in distortion.
I've just discovered how useful volume boosts are. Last weekend I was working out some new patches for some electronic cover songs, and I found a pretty nifty setting using my OFD, MWBD2 and Manta. With each sweep of the hothand the OFD goes from 0 volume to max volume, the MWBD2 blends from clean with high cut to octave up boosting the upper octave frequencies and the manta does a low pass filter sweep. This seems to get me a much more detailed wobble sound than just applying a low pass filter. I wanted to record it but I haven't had the time to do so, it's been a busy week. I'll try to export the .scn file tomorrow or something when I've time to plug into my computer (wish I could do it from phone!)
I'm also trying to work out a patch that makes use of the volume boost trick to imitate a bowed string attack. After that patch idea I just mentioned, I realized that using the hothand is a much more versatile way to control the attack envelope (via hothand control of the pedal's "volume knob") than the volume knob on the bass itself. I'm guessing with appropriate settings on the MWBD Pro and Manta to simulate how the note timbre changes as bowing pressure increases, I should be able to get a fairly convincing bowed string sound. I suppose someone more familiar with brass instruments could apply this to create brass instrument notes too.