I get great results using Comprehensive Video (www.compvideo.com, 800-431-6000, South Hackensack, NJ)Female XLR to 2 male XLRs Y-adaptor cables (part number XLRJ-2XLRP) at the amp end of my 8-meter Cello XLR-to-XLR cables from preamp to amp. This Comprehensive Video cable is very low in capacitance. The legs of the Y are about one foot long, allowing direct connection of the legs of the Y to stacked monoblocks for biamping.
Yes, you have more connections in the signal path this way, but your preamp is not loaded by a lot of extra cable capacitance from an extra set of interconnects and the Y-adaptors are much cheaper than an extra set of equal-quality interconnects. The extra capacitance of another set of interconnects can cause audible degradation since the amp input impedence seen by the preamp is halved when you use Y-adaptors. Two of these Y-adaptors cost about $50, so you don't have much to lose trying this method. I use ProGold spray on all connections. Comprehensive Video also makes single ended Y-adaptors of the same type.