Help choosing coupling caps

Construction of SIO is somewhat ambiguous, as Mundorf mentions both polyprop and metalized paper construction:

"Our state-of-the-art metallised Polypropylen foils make it possible to maintain extremely exacting production tolerances that cannot be achieved with traditional oil/paper capacitor designs. This is also the first time that the benefits of oil-impregnated capacitor design have been successfully combined with the well-known long-term stability of metallised paper and internal series wiring for induction-free performance."

I believe the Silver/Gold version is dry, which may account for its temp rating to 85C, as compared to 65C for the oil versions. 65C could be problematic in a hot chassis.

After a bit of humming and hawing i'm going to try out the k40 PIO replacing the coupling caps in my tube amps.
These have great potential.... we shall soon find out

Thanks to everyone that posted ..your input is very much appreciated

Quick update
I used the mundorfs in my cdp and I really like the sound now hoping to get a similar performance with the Russian Caps in my Amps
IMO Russian caps in combination with Teflons is a very good mix

FWIW...I have had good results with Mundorf M-Supreme caps. Very detailed,increased clarity,and smooth as silk with no brightness....relaxed. The supreme are physically a smaller footprint than the SIO caps. Exceptional in my tube dac.

Not surprised you like the Mundorfs in the CDP, I thought they would have been perfect in my two prior tubed DACS. Not so great in SS digital.