I would say it depends on the wire. I use Kimber 4VS with the Salk HT2-TL and AVA Synergy 450 amp and have tried three different configurations:
1.) Single run (2-13 AWG) with jumper - OK
2.) Double run (2-10 AWG) without jumper - Better with deeper bass
3.) Double run with jumpers - Best bass of all, the Seas Excel W18E001 drivers will use everything you give them, don't hold them back with small gauge wires.
In all three configurations the mids and highs did not change, just the lowest of low bass. Test recording used: Mickey Hart's Planet Drum - Temple Caves, the low drum beats should fill your room, make you smile and say "I didn't know my speakers could play this low".
Wayne