well iv just picked up a pigtronix envelope phaser pedal, and have to say im very impressed with it. it has the mod done to it so you can have the phaser and filter on at the same time, and to contradict what someone else has wrote in this thread, it works superbly. The filter has a very good feature; it has a seperate trigger jack, so that the envelope can be triggered by your clean bass sound, but will modulate your effected sound, for example i have my signal split, clean bass going into the trigger jack on the pigtronix, and then my clean signal going into effects and then into the pigtronixs' main input. so when a fuzz pedal is on, the envelope is triggered by the clean bass signal, but applies the effect to the fuzz, and thus sounds brilliant with no dynamics lost. Bloody brilliant. im not sure how many other filters have a feature like this!
sorry bit OT there, but yeah i think phasers work great with filters, not sure which way round the chain is in the pigronix, but i imagine the phaser is after the filter alternativly get the pigtronix! i imagine it would work fantastically with the BMS when triggered by your clean bass signal, although its a bit pricey so depends on your budget