quiet frankly I just know the k&k, for standard systems, which is pretty decent in sound imho
but at least worth a thought is this one or something comparable
http://www.lacemusic.com/USAB.php
can be installed like a archtop pickup, with a bit of work too, lets call that floating for now
and then you get a quiet versatile instrument, depending on the position
or just tape/glue it on
it's more on the side of an electric sound than acoustic, but then again, most plywood doghouses dont sound good anyhow...
so an EQ is needed anyhow...
I installed one of those before, and played it on stage a while later too, not my bass
it does sound somewhat similar to a doublebass
I go with my fretless jazzy though, preferably
best acoustic bass sound possible
btw, the guy I installed it for played the first half of the first gig after installing it without turning his amp on, without noticing
sometimes the bass player is just there to make the stage look a bit more crowded...
best
j