I went to the Talk Bass forum and received this to my question: You want your buffering done as early in the signal chain as possible. If you can't put the buffer directly on the bass, then put it on your strap, to minimize the length of cable necessary. If you have to use more than a few feet of cable before reaching the buffer, then there will be tone suck.
Sounds like he is saying the the distance from the preamp and instrument should be short as possible with a piezo p/u. I wonder how much tone suck is there and how important?
I can share some info regarding buffering and impedance in general, and you can apply that to any audio signal...bass or otherwise...
With both piezo and magnetic pickups, for longer cable runs there may be an issue with tone suck, but this is primarily due to the capacitance and built-in resistance of copper cable. Too long of a cable without some kind of correction and/or boost and the electrons simply cannot flow any further.
Piezo pickups also have an issue with buffering and impedance which I will discuss below.
This buffering problem is also made worse if you have a huge effect chain. Each effect causes an 'insertion loss', which means that the output signal is going to be less than the input signal, even with pedals that offer 'true bypass'.
This occurs with everything that uses copper cable. lets say you have 10' of cable coming from your instrument, going into a signal chain of 10 effects, each connected with those 6" patch cords, and then another 10' of cable going to your amp or DI. Each connected device causes insertion loss that can be as much as 3-5 db. the db (or decibel) scale is logarithmic. So 3 db of loss is a 1000x reduction (10 x 10 x 10=1000) in output level. This is mitigated somewhat by the input impedance of each device expecting a 10kohm signal but outputting an impedance closer to 1kohm. However, by the time you get to the end of the signal chain, you still have a net loss, and therefore tone suck.
There are 2-3 ways to fix this problem:
1. put a 'buffer pedal' at both the start and end of the effects signal chain, which boost the signal going IN to the chain, and can make-up the loss encountered at the end, coming OUT of the chain. Decent Buffer pedals can be found for as low as ~$70, or you can build your own from parts using a soldering iron, following any of several public-domain schematics, for about $15 parts cost and about an hour of your time. You can also buy them in kit form and solder it together yourself for about $35 for the kit.
2. You can use a preamp or 'boost' pedal as the first device in the effect chain, and a buffer pedal at the end, which will have a similar effect as #1
3. You can use the same as in #2, but add an 'active' DI box that has an impedance-matching transformer inside which will also have a similar effect as #1
Having said all that, MOST external preamp units on the market today, by default combine the buffer circuit inside the preamp, as well as also having a DI function with an XLR output, so you might be able to get by with an external preamp, like so many have been doing successfully for years.
As far as how this interacts specifically with a piezo pickup, and buffering and impedance, I'd like to refer you to my detailed posts over in another recent thread where I tried to explain those concerns with several solution options. While this is not the same question you asked, but the signaling issues are inter-related and might help in understanding all of this stuff.
Please take a look over here:
http://forum.ukuleleunderground.com/showthread.php?110167-Preamp-for-Electric-Acoustic
Please let me know if this information is useful to you.
Booli