I've used both Kaplan Cables and Triode Wire Labs on my McCormack amp. The Kaplan is a little warmer sounding, but could be a bit much depending on the tubes in your Modwright. The TWL cable is clean, transparent and works well if you are using warmer sounding tubes in your preamp.
Both are excellent cables, depending on the sound you are after.
Both are excellent cables, depending on the sound you are after.