There are some clips below of a recent gig where I was using a Wilson K1 pickup without a preamp into a Carvin BX500 through a Bergantino EX112. When I play in a big band setting, I usually just run into an MXR micro amp as a preamp to boost the signal into either my Carvin or Epifani UL502 to get a little more juice and it sounds just as articulate and full without being boomy.
My first pup was an Underwood, which was nice. Then I used a Realist for a while and liked it, but found with the bass at the time that I had, the top was not responsive enough to really get a good sound out of it. The Realist really (IMO) needs a bass with a great top to shine. Then I went to a Wilson K4 and used it for years and really loved it's flexibility, especially in Tokyo, where I use back line rigs a lot and having the ability to adjust each string was helpful in addition to the strong signal it produced (no preamp needed with it). However, I bought the K1 after sampling one at the Bass Center in Shin-Okubo a few months ago and I have been uber pleased. It doesn't have quite the same output of the K4, but it does have a much more natural sound, but still with a lot of clarity and depth that was produced by the K4. http://www.youtube.com/watch?v=1oHkfcA1Vk4&safe=active
Anyway, if you are interested in a K1 here are some clips to check out before you pay for one. I am using Velvet Blues BTW on a Lemur Music Laguna bass.