My favorite trick for treble glare - 4 6mm girasol opal beads tied together with flexible beading cord and slipped over the speaker cables about 3-4 inches from the speaker terminals - adjustment to taste. This in essence is a cable "choke" but much more refined than the ferrite versions. The result is a sound very much like that of tubes. Four beads fit over my 16 gauge "western electric" cloth cables. Larger diameter cables require more beads for making the "ring."
This is not technically "opal" but is called that because of the way it handles light. The beads below are 8mm diameter, and it is sometimes hard to find them in the smaller sizes. 8mm diameters will work for larger diameter cable or even the thinner gauges - it is just more difficult to make the "ring" of beads to encircle the cable with some spatial uniformity.