I use the Cerulean biwire cables with a tube amp (Cary SLI-80) and Concentus Lyra speakers. The previous cable was a single-wire AZ Satori. The Concentus speakers are sweet but lack ultimate transparency and have terrific bass. The Cerulean cables improved the picture - they tightened the bass, midrange became cleaner and clearer and less bloated.
Much impressed, I ordered the Cerulean interconnects but was not impressed that much - they lent some dryness to the overall sonic picture. I'm currently using the Cerulean speaker cables and Kimber Select KS-1021 interconnects with excellent results.