There's nothing wrong with Holcos, and The Parts Connection has the best prices on them that I've seen. If you consider Vishay or Caddock, be aware that there are different types, some very highly regarded, others not. E.g. I was informed by one company president that certain Caddocks aren't much good, though he sees other Caddocks as the best choice for an amplifier upgrade he offers. I have one passive preamp using Shallco switches in which I have tantalum resistors, said to be the ones used in top Audio Note Japan gear. I only need six positions, so the high price didn't kill me. I did very careful comparisons with Holcos, which I like a lot, and liked the tants better--a very "natural" sound, maybe even with tubelike "bloom" compared to metal films. In the end, it's very much a matter of taste. You could do some comparison testing with fixed attenuation networks, as I did before settling on the tants. All you need is two pairs of RCA jacks and four resistors, for such a network.
