One issue I'm getting more familiar with when I do any slapping - usually only one or two songs over a full gig - is that I can't slap so fast while on stage if I want what I'm playing to have enough clarity. At home I can slap around rather fast, but there are no other instruments making sound and it's much easier to hear all the quick little notes when I'm popping and plucking around in that setting.
When recently playing with the band, I've been trying to slow down a little more and slap with some more melodic hooks, at least at the outset of a little solo. If my passive tone control is cut back at all and I'm about to slap, I'll open that up to get more bite when I'm playing those more snappy sounds that need that crisp attack. But if I go for too many notes or overly acrobatic stuff that isn't especially musical, it just gets lost in the room.
Now that I'm slapping in a lower gear and the folks at our shows can hear what I'm playing, they're diggin' it a LOT more than in the past. A while ago when I'd slap-solo a little bit, I'd get maybe a polite whoop or two after ripping away on something that felt good and sounded right to me. But I eventually got the feeling that the super fast stuff just couldn't reach the ears out in the room.
I got thinking on this issue after catching a few interviews of both bass and guitar players through recent years. While the studio can catch and reproduce almost everything that somebody might play, the common sentiment seems to be that playing live is more tricky. We can overcook it more easily without knowing it. Billy Sheehan and George Lynch were two guys among several who pointed this out.
I don't know a specific gear solution to help with delivering a live slap sound that's more potent, but I like the idea of have an eq or something at the ready with a quick stomp. We can't waste time killing the groove while noodling with amp settings before we slap-ify. I just offered this thought because playing a little less has been a huge boost (Ha!!... boost, get it?) for what little slapping I do with the band regardless of how my eq is set.
Oh - and don't forget your envelope filter. Uncle Bootsy will thank you later