I have had a few different sets of strings on the AFR. The bass has a very different sound with each set. I would like to attribute that to the piezo system. It really gives the sound of the string, mixing with the magnets more traditional midrange heavy tone.
The Stock XL strings were surprisingly good. I do not usually like XLs, or nickel. My skin killed these strings in 3 weeks.
Nickel Elixirs were next up and are extremely bright and sizzling. Much finger noise on every string. They came off quickly as they are more suited to darker sounding Basses like a Warwick.
Ernie Ball Group V flats followed up the Elixirs. Decent sounding string, but on the modern side of flats. They had a surprising amount of treble content and that is not what I wanted. They may have been a good string if they broke in but they began to rust in 2 weeks and that was enough for me to say goodbye.
I settled with my old favorite strings, stainless steel DR Low Riders, in the lightest gauge offered for a 5. Just perfect. Far less brightness than the Elixirs, smoother midrange than the Group V flats. These strings give the midrange a different growl. Overall the tone of these strings seems to smooth out the somewhat aggressive mids of the AFR.
It is by far my favorite bass in 23 years of playing.