I'd like to add to this discussion as I have just replaced AP Crystal Oval with Nordost Quattro-fil on the run from turntable to pre-amp.
Better clarity is very evident, as well as more highs. Perhaps the most surprisingly and enjoyable benefit was the more evident 'timbre' of the notes....especially bass notes (as also mentioned by Jond). Stand-up bass on Norah Jones' LP for example, is very life-like and real.
That said, I've also added Nordost Valhalla to my Linn Ikemi CD player, and must say the Valhalla is even more open, airy, and I am getting waaaay more clarity and range in the upper end (perhaps CD vs. Turntable/cartridge diff?)
So, if you like Quattro-fil, you'll love Valhalla. The best I have ever heard. Magical. Expensive. Worth it.