Preamp Output Capacitor: Mundorf Supreme vs. Supreme Silver Oil

The sound character of the particular output capacitor will have a much greater effect than the different measured cutoff frequency with a 100K load (23 vs 8 Hz).  
For example, a Mundorf Silver/Gold/Oil sounds “thin” regardless of cutoff frequency; an older InfiniCap would sound even more thin and lightweight.  On the other hand, a .68uf Copper V-Cap with a 100K load will have deep, powerful, full-bodied bass despite the measured response being down 3db at 23 Hz.

AG, not necessarily.  A 0.68uf cap into a 100K loaf will have a rolloff that is -3 dB at 23 Hz.  That is not going to sound “thin” on most systems.  The 2uf cap extends the -3 dB freq to 8 Hz.  There would be virtually no sonic difference between these two caps provided they are otherwise identical (same brand, same model) at least on most systems.

You're right!  That should teach me to do math in my head.  I dropped a digit.  

Of course that makes the issue of the value of the cap even less significant sonically.  With tube gear where the input impedance is typically 100K or more, a 0.68uf coupling cap is fine.  

Not everyone agrees that a small bypass cap improves sound quality.  I have tried bypass caps in all sorts of applications going back literally 40 years and I haven’t found a single instance where the bypass improved sound quality.  The bypass certainly changes the sound; usually the bypass makes the sound brighter, leaner and less coherent.  I much prefer the sound of a single quality cap like a Copper V-Cap over any combination of caps with a bypass.

You may reach a different conclusion so by all means try it yourself, but don’t be surprised if you tire of the sound with bypass caps.

If I am going to be in a minority, I don’t mind having Ralph from Atmasphere in my corner.  Over the years I have noticed that Ralph’s observations often agree with my own.  
That said, I am not sure I agree with Ralph’s implication that problems with bypass caps are more of a problem on highly resolving systems.  As I said in my post on the previous page, I have experimented with bypass caps for 40 years and my gear from way back then would not be considered highly resolving by today’s standards, yet the sonic problems with bypass caps were evident in all of my systems.

I think the different reactions to bypass caps are more related to different listening priorities.  To my ears the positive things that bypass caps can sometimes add can be described as “Hifi spectacular” artifacts—-bigger soundstage, more specific imaging and seemingly more inner detail.  Certainly I am not opposed to hearing more detail, but for me the “improvements” caused by bypass caps are artificial.  They come at the expense of a skewed tonal balance where the HFs are emphasized and have an artificial sheen or glaze, and the upper bass/lower midrange becomes lean and lacking in natural warmth.  The degree of skewed balance changes with different caps but the direction is always the same.  
In addition bypass caps make the sound less coherent: music sounds like it’s coming from a 3-way speaker rather than a single driver.
Furthermore, with a truly high resolving system I find I hear just as much inner detail without bypass caps.  The detail is just less hyped.

Some people hear and like the “Hifi spectacular” sound and perhaps don’t notice or aren’t bothered by the negatives.  Other people find the more spectacular sound artificial and find these qualities make the music less natural.  
At the end of the day, if you like the sound with bypass caps then go for it.  But you really should try removing the bypass caps at some point after they are fully broken in and you are fully used to the sound.  You might just find you actually prefer the sound without the bypass caps.