I've got the Sadowsky flats (SBF45B) on my Yamaha RBX775. I played them for quite some time (10 or so months

) before I finally got my Sansamp in.
Now that I have the pre-amp I've noticed they are.... dead or muddy sounding and I'm about to be buying new strings, so I'm a tad confused.
I love the feel of the flats, but I don't know exactly what they will sound like now that I'm not going straight in. I guess I'm looking for more of a "brighter" flat. Are Sadowsky's a good choice again?