Preamp Output Capacitor: Mundorf Supreme vs. Supreme Silver Oil

I tried the Duelund .01uF tinned copper cast bypass caps in three positions and came to different conclusions each time. 

I liked them on the .47uF interstage coupling caps of my Coincident Frankenstein 300b monos.  Thought the sound got more real and natural with them in the chain.  Couldn't hear them at all over the 1uF Miflex output capacitor on my Don Sach's 6SN7 preamp.  And heard the smearing effect when I put them on the 4.7uF cap (Clarity at the time) used as a high pass on my Coincident PRE's tweeter.  

I forgot to add that IMO part of the issue with bypass caps has to do with the size of the coupling cap you are bypassing. Generally speaking I've not liked what larger coupling caps do as they impose more coloration. But in some cases they have to be used- such as at the output of many tube preamps and also driving output tubes in a power amp. For this reason I've avoided coupling caps in these specific areas (instead I employ direct-coupling) as this allows me to use much smaller values overall. I can easily see resorting to bypass caps in the case of larger caps- 1uf and above in particular.

Exactly Ralph, my Amps use four 2.2 value caps per monoblock, one for each tube. When running just a single large cap the sound is definitely shelved off in the highs, scymbals sound rounded off for an example. Adding .22 value caps opens the amps up, while still sounding very clear and clean, it just adds some sparkle up top making the system sound less dark.