I used all Northcreek caps, which are no longer available. I believe the most cost effective alternative using currently avaliable caps would be Sonicaps, but they are quite a bit more expensive than the Northcreeks that I used. The effect of this kind of upgrade will be an overall smoothing of the treble with reduced glare and a more audible and realistic decay of percussive sounds like cymbals.

A more cost effective option that would result in an audible improvement would be to use a "cascade" of Solens and Sonicaps to replace each individual cap. For example, you could replace a 22uF cap with 12uF and 8uF Solens plus a 2uF Sonicap, all wired in parallel. I prefer this to traditional "bypassing" where you might combine a 22uF Solen with a 0.1uF premium cap. I can't hear the difference with this kind of bypassing, but I can hear the difference with cascaded caps. You will want to use a single premium quality cap to replace any cap whose value is less than 1uF, like the 0.47uF tweeter L Pad bypass cap.