I have an EAR 864 preamp, which includes an 834p phono stage. I used Rel RT polystyrene caps on the phono stage many years ago and it was a noticeable improvement over the stock caps (I think they were Orange Drops). The line stage also had Orange Drops, but I changed those with V-Caps (tinfoil) at about the same time. Spatial information was improved. High frequencies were more detailed and clear. However, over time and with different monitors, I found them fatiguing.
A few weeks ago I opened her up again and removed the V-Caps and put Miflex KPCU-1 in their place. I got the idea when reading through the Troels Gravesen website. I believe he used Jupiter caps, but of a design with similar ingredients. (Wax/Copper Foil/Oil/Polypropylene)
The end result was beyond what I had hoped for. Plenty of spatial information, deeper and wider soundstage. Low frequencies were bigger, heftier , fulsome and dynamic. The perceived frequency response was more balanced.
I recommend the Miflex if this is the sound you are after.
If I had to characterize the Rel RT Polystyrene, I would say that they are clean and very clear. Lacking glare or dullness. Well balanced. Perhaps a bit dry. I hope this doesn't sound too weird, but polystyrene has a neutral resonance, not unlike rubbing a Styrofoam cup.
