Attenuators can't fix your problem. Its just that simple. You need to understand the difference between gain and volume. You have a gain issue, and that means you have to fix the problem with gain. The high output of your phono cart is overdriving the input on your phono preamp. If you use volume/attenuators, the distortion will still be there no matter how much you lower the volume.
Anything involving gain is on the input of a component, and anything involving volume/attenuation is always on the output of a component. They are 2 separate things. You can only damage the signal with excess gain. Volume/attenuation can't alter or damage the signal in any way (aside from whatever slight coloration that may happen when the signal passes through the it). Its like having a record with a lot of scratches. If you lower the volume, the scratches are still there. You need to get a different phono pre or a different cartridge. Its your only option.
As always, sound quality is subjective. That said, a LOMC cart should make a significant difference in sound quality. And its the type of difference I think you'll be very happy with. I can't make any guarantees, but I think there's a far greater chance you will like a new cart, than not like it.