Well - I suppose it's down to the player to a huge degree - I prefer bridge pickup, tone all the way up, and my 5 str JB sounds OK, but only just OK. It's got too high an action for good slap, so I'd swap it for my other 5 or even the 6 string basses because they have a lower action and make a better slappy sound. Then - once recorded - I'll tweak the EQ to make it sit with what else is in the track.

I agree with Paulears and would add that once the instrument is dialed in and you are getting the sound in the room you need, then you have to decide how "percussive" you want it to sound. Compression will be critical with slap bass. You can use a transient designer to get the attacks you want and I will typically use a parallel channel to get the release I want out of this type of bass sound. I may even make a third channel to control sub lows.

The Transient Designer from SPL Audio is excellent. The hardware version is a bit nicer (faster and a bit cleaner) but both hardware and plugin are excellent for dialing in super cool attacks with that slap sound. The Transient Designer is also awesome on snares too.

I am, in love with my Transient Designer UAD plug in, very cool and useful tool.

Here's a trick I do all the time when slap bass is required.
Besides the normal Di, and Amp, I tape a Countryman ISO-MAX mic to the bass body.
Usually listen with my ear to find the best most resonant spot on the body itself, and then tape the mic there.
But you gotta make sure it's not in a spot where the player or his close might rub against it.
It takes a few tries to get it in the right spot, but totally worth the effort...
Then blend to taste
Here's a clip (mp3) of a song I'm actually mixing today, recorded using exactly that process~!

Nobtwiddler, post: 468190, member: 52450 wrote:
Here's a trick I do all the time when slap bass is required.
Besides the normal Di, and Amp, I tape a Countryman ISO-MAX mic to the bass body.
Usually listen with my ear to find the best most resonant spot on the body itself, and then tape the mic there.
But you gotta make sure it's not in a spot where the player or his close might rub against it.
It takes a few tries to get it in the right spot, but totally worth the effort...
Then blend to taste
Here's a clip (mp3) of a song I'm actually mixing today, recorded using exactly that process~!

Wow!. That is an awesome tip!

Nobtwiddler, post: 468190, member: 52450 wrote:
Here's a trick I do all the time when slap bass is required.
Besides the normal Di, and Amp, I tape a Countryman ISO-MAX mic to the bass body.
Usually listen with my ear to find the best most resonant spot on the body itself, and then tape the mic there.
But you gotta make sure it's not in a spot where the player or his close might rub against it.
It takes a few tries to get it in the right spot, but totally worth the effort...
Then blend to taste
Here's a clip (mp3) of a song I'm actually mixing today, recorded using exactly that process~!

Sounds great!