They sound the way I wanted, smooth, lower toned, like a sports sedan.
a nice growl with rapid acceleration, reassuring background hum when cruising, no rasp or drone.
it's not easy to say if performance is improved, I have no way to measure it, But it feel better. Economy is improoved (even though I might be using it harder) by about 6% on the 128. Not had time to evaluate the 2004 325Xi economy yet.