Grannyring, I have used Mundorf Supreme (regular version, not the Silver, Silver/Oil or Silver/Gold/Oil) in my speaker crossovers for several years. I find it to be a very nice sounding musical cap but with some fairly obvious tonal colorations. It has a rich warm mid bass and slightly soft highs.
I have tried many different bypass caps in an effort to make the Mundorf more neutral sounding, but to date nothing has sounded better overall than the solo Mundorf. Most bypass caps sacrifice the smooth coherent sound of the Mundorf by itself. For a while I thought I had a winner with a 1uf Sonicap Platinum bypass. The SP has a solid low end and fast, clean, airy highs. (The SP is well broken in since I have used it for years in various projects.). Just this morning, I tried removing the SP for the first time in about two weeks, and sure enough I still prefer the Mundorf on its own. The SP, as good as it is, makes the Mundorf less coherent; it no longer speaks with the same voice.
The only real solution is to replace the Mundorf with a Duelund CAST. That's what I did last year with the high-pass cap. A single Duelund (fully broken in) in that spot sounds much better than any other single cap or cap cocktail that I tried for the high-pass. So I figure it's only a matter of time before I buy another big Duelund for the low-pass. I just wish they weren't so expensive.
By the way, I tried a .47uf Duelund as a bypass on the Mundorf in the woofer xover, and it was even less coherent than the Sonicap Platinum bypass. Also, you might think a more expensive Mundorf like a S/G/O would make a nice match with a regular Supreme, but they didn't work out at all. Too much emphasis on the highs and a loss of coherency. The S/G/O sounds pretty nice by itself but not as a bypass.