I have a 508.20, however, it's been modified w/Blackgates & Schottky's. I settled on a TG Audio 688 after trying the SLVR, only because the SLVR was a tad bit bright for me. So, I second TG Audio cables.
As for the differences between a good aftermarket PC & stock, in addition to what Vikvilkhu said, I think you'll find the soundstage shrinks, bass isn't tight & the overall presence suffers.
As for the differences between a good aftermarket PC & stock, in addition to what Vikvilkhu said, I think you'll find the soundstage shrinks, bass isn't tight & the overall presence suffers.