The improvement you heard by paralleling (aka, "shotgunning") the two speaker cables and jumpering at the speaker posts would indicate that the wire gauge used in your original biwire configuration was not adequate. There might be a slight improvement over your current setup by running the original biwire configuratrion (without the jumper) using larger gauge wire but, if you're happy with the sound, leave it as is.
Congrats on finding a no-cost improvement. Those are the best kind.