I also tried surplus Aerovox motor runs in the 8 and 20 uF posiitons of the 1600 Hz crossover and didn't care for the way they 'darkened' the sound and smoothed over detail.

Just for fun, the other night, I priced VH Teflons for my Cornet II board and the total, $900, was 3 times the total parts cost! For a possible incremental improvement? I think not. Perhaps just $100 for .10 by-passes? I remain unconvinced that by-passing has any reward and, in fact, there's a school of thought that says it has a deleterious effect on the electrical function of the main cap.

"A capacitor stores and releases charge over time so that only the ever changing audio signal will pass through it on the way to the outputs, blocking the DC from the tube. Differing values of capacitor charge and discharge in different times. The two different values are said to have different time constants. The small bypass capacitor charges and discharges faster than the larger value cap, thus it affects the higher frequency sounds. The effect of this is the render the highs brighter since they have been stretched over the two different time constants."
-Matthew Anker, SACDMods.com; E.E. student and well-known modifier

I can easily recall the clearly audible improvement in changing the Bottlehead Paramour coupling cap from a ceramic to a Solen Film cap and the Solen, in the Pi attenuation circuit to an Auricap. There was no such change with the Mundorf. Some have said that the Auricap sounds bright and/or brittle. I haven't heard that but I haven't heard sounds above 14kHz for years! The Obbligato oil caps may be smoother on top than the Auricaps and equally 'musical' throughout the audio band. I find them at least equal in the crossover of the Batspeakers, and, in larger values represent a cost savings.