I'm not a fan of the sound of under the saddle peizos, and the ugly plastic electronics boxes that are cut into the body. But with limited options for acoustic bass guitars here, when I stumbled on a Takamine with a piezo, and went for it. It's handy having it, most often I never plug it in and it just a tuner (the battery went abut a year ago and it's telling that I haven't bothered investing in a rechargeable yet). I added tapewound stings and it sound lovely, and although smoother than rounds s less obvious sliding nose, there is a little that I don't like and the the under the saddle seams to picks this up quite well.
 
I've just bought a Guild that unusually came with a sound hole pick-up built in (so no plastic box), and I am loving it's pick-up sound. So I m back to wondering about a different solution for my ABG. Soundhole pick-up for ABG dn't seem to exist, I've had a look to see if Dog-ear pickups are available for Hollow bodied electric basses, to adapt, but it seems this transducer option may be the way to go.
 
http://kksound.com/products/purebass.php
 
If I pull out the old under the saddle, I'm left with a hole I can only think of covering with some tortoise shell pick-guard plastic. But I think I should just leave it in. My options seem to be.
 
1. Remove the peizo's output jack, and replace with the transducers. Leaving the electronics as just a tuner.
2. Add a second output hole, which I am reluctant to do, as adding more holes seems a step backwards, but would increase flexiblity. 
3. Is really the motivation to post a question. Can I wire the Transducer into the existing electronics designed for the piezo? The Transducer is said t be a lower output, but surely higher than the piezo's as it requires the pre-amp. This would give me the pre-amp, EQ and a tuner and a different sound. 
 
 

You can run a piezo equipped guitar thru a "body resonance" IR... and it does *wonders* for the sound.
Gets rid of that quacky/smacky sound... and sounds a whole lot more like an acoustic guitar.
 
There's a free collection of Taylor "body resonance" IRs (mic'd with several different mic options).
You can download those... and use a convolution plugin to load one and play thru it.
 
If you're talking live, one of the better current-generation modelers (Axe-FX/AX8, Helix, Amplifire, HeadRush, GT-1000) can be used to load the Taylor "body resonance" IRs.
 
This sounds a whole lot better than it should.
In fact, with a bit of tweaking, you can used body resonance IRs and EQ to create "acoustic simulation" patches for guitars with standard (magnetic) pickups.
For several years, I would only buy electric guitars that were equipped with Piezo in the bridge.
After becoming proficient using this technique, I no longer worry about guitars having Piezo.

This is for a bass, so it's not so 'quacky' as such. I'm looking t get the Bass itself closer to what I want, than resort to software.   My new Guild is a small bodied bodied guitar, but has a soundhole humbucker so no worries there.
 
Maybe my post was too long, but do you have any thoughts on
"3. Is really the motivation to post a question. Can I wire the Transducer into the existing electronics designed for the piezo? The Transducer is said to be a lower output, but surely higher than the piezo's as it requires the pre-amp. This would give me the pre-amp, EQ and a tuner and a different sound. "
 
Since writing the post found the Jack plug out has 3 small holding screws, So if the K&K can't use this, then maybe I should just opt for option 2 (add a second output hole). But some reviews of the 'K&K Pure mini' say it's better with a preamp, so I'm still wondering if the 'K&K pure' will; benefit from using the existing Piezo's preamp, saving me touching the output jack. of course  I can just try it when it comes, but I'm just checking if anyone know if it's advisable.  
 
 

Good question Kami, and nice answer Jim. You have just given me some ideas to push toward a better sound with my piezo equipped acoustic.

Sounds to me like you can try the KK with the piezo electronics and see how it works out. No new holes and reversible. If you don't like it, put the piezo back in.
 
However, I DO know that piezo's require preamps not for gain (the output level of a piezo is plenty big) but for impedance. Piezos need a very high impedance load to sound the best. The higher the better (I've used 10M preamps for those). The KKs will have no problem with that, if that's all the preamp is doing. If Takamine has also added some EQ so "soften" the sound of the piezo, then that would affect the KK as well, which you may not want. But I bet they didn't do that. The preamp is probably only there to provide the proper load impedance., so you should be good.
 
But, I need to warn you about the KKs. They are very sensitive and pick up all noises, not just string sounds. Things like arms rubbing the side while you play, picks/fingernails hitting the top, shirts rubbing the back. It's also VERY sensitive to the tribolelectric effect (hearing noises as the cable moves). External cables aren't such a big deal if you use the internal preamp (which acts to isolate the external cable from transducer) but you'll need to be very careful how to suspend the internal cable inside the guitar. Don't let it hit any of the sides or top or anything that flexes. Tack it down at the joints/corners. I ended up sending my KKs back. I just couldn't isolate these external noises well enough.

Cool thanks (I've been warned). There is a bybass EQ on the unit, but I guess you are suggesting something possibly outside this control.

I've additionally though about connecting a male jack to the input of the TK-40B, and then I just use the output (female) jack intact on the K&K, and connect it up (so the K&K is reversible). Thanks for the warning about cable noise, I'll be sure to secure the old disconnected Piezo cables, added jacks, stray wires and cats. 

 
 
 

FWIW, Before modding the bass (sorry I missed that the first time), you might want to take it to a music store that has a Fishman Aura (small hardware preamp that will do similar to what I mentioned above).
 
https://www.fishman.com/products/series/aura/aura-spectrum-di-preamp/
 

That's out of my price range, and won't be available here. It's in Meng's shop 900Km south

I’d suggest leaving the undersaddle piezo strip where it is. They are surprisingly easy to damage, and the damage is often undetectable until they’re refitted. Another problem is that undersaddle piezos rely on the pressure applied to them by each string and the base of the saddle slot to be correct and properly balanced. Otherwise their response to each string can vary a lot.

Another reason to leave it in is that removing it will lower the saddle height and change the break angle of the strings as they pass over the saddle to the anchor points in the bridge. If the action or break angle ends up too low that means making a new saddle.

Sometimes the manufacturer hasn’t fitted the strip properly or the base of the saddle and slot need fine adjustment to get them to work at their best, but that’s not the sort of thing to explain in a forum post, or to attempt unless you’re confident about your woodworking ability.

Piezos usually benefit from being run into a compressor and a decent equaliser that’s more adjustable than the built-in preamps - and this can compensate for a lot of issues with them. I suggest running the piezo into the DAW and experimenting with compression and eq to see if it can be made to sound better. If it can, that’s fine unless you need to use the bass live, in which case a compressor pedal (preferably not an MXR or Keeley where bass is concerned) and a graphic eq pedal can often work wonders.

Thanks for the input. I wasn't thinking of removing the Piezo, just disconnecting it. When it came the action was too high after truss rod adjustment, and the saddle came with a number of shims, some angled. I've removed 2 or three I really happy with the height, so I'm not keen on facing all that again.  The base of the saddle isn't flat like a standard saddle, but shaped to fit the piezo. So if I wanted t remove the piezo, I'd have t change the saddle too