I would not discount the suggestion made by @almarg .
Have you optimised the impedance between amp and speaker by trying both 4ohm and 8ohm taps?
Can you tell us what amp you're using and tube type? A tube change is more likely to increase high frequency energy rather than changing cables; ie, NOS Sylvania tubes are known for their extended highs with great detail.
Have you optimised the impedance between amp and speaker by trying both 4ohm and 8ohm taps?
Can you tell us what amp you're using and tube type? A tube change is more likely to increase high frequency energy rather than changing cables; ie, NOS Sylvania tubes are known for their extended highs with great detail.