It's already difficult enough to find a decent pedalboard. The other difficulty is to find a module to be controlled by the pedalboard. Thus far, I've found the best choice by far is the Evolver Desktop. The key is number of oscillators; you need as many as possible, and the Evolver's 4 are a good start. As for extant modules, perhaps the Toraiz AS-1 would be a good choice, although it offers only 2 oscillators. Its single LFO shouldn't be a problem since, for bass purposes, you'd only need to modulate the pulse width or the filter. And by the way, sub oscillators are generally not useful, especially if they're square or triangle, the reason being that, due to the lower range the instrument is set to, a sub oscillator needs to be less bassy - either a sawtooth or a narrow pulse. Otherwise, the boominess is overwhelming and the clarity of pitch is muffled.