I have read a lot here about what various folks have put in their 55-01's to upgrade their tone. It's all a matter of preference and I'm on the fence because I do actually like the MK1's, but the top is a little harsh and the bottom not very tight. They are okay and I seem to be able to get by with them live thanks to my Sansamp Bass driver. On the fence if I should just change over to Bart MK5 pickups and leave the preamp or change out the preamp and leave the pickups. I'm pretty sure I'll get the MK5's eventually either way and wonder how they will work with either a Lakland LH3 peamp, the Bart 5.2 or the Aguilar. If anyone has any experience with the MK5's and any of those preamps, I'd love to hear your feedback. All three pre's offer active / passive and have some sort of way to change the mid frequency either with a push pull or dip switches on the Lakland. Anyone using the barts I'd be curious to know if you're running them parallel or in series and how you like the sound. Thanks guys!