The best, and unfortunately most expensive, are Duelund. The thing however is to use them judiciously depending on exactly where they appear in a circuit. A speaker designer I know uses them all the time but only at critical places such as in the signal path. At other places cheaper stuff like Erse or if you want to up it a bit Obligato will yield virtually the same result. If money is an issue Obligato bypassed by Duelund is very good.
Thanks
Bill
Thanks
Bill