There do not seem to alot of cable brands that offer this by default however there is another pair of Spectron monos up for sale on Audiogon right now where the seller is picturing a set of Synergistic Y-splitters for XLR cabling. You have not said what cable brand you intend to purchase but I would agree that (at least over the years in my systems), XLR yields the best results. If it is a fully balanced pre-amp then this is all the more true (IMHO). I'd suggest determining which interconnects you intend to utilize and asking that manufacturer if they will make a Y-splitter XLR cable for you as a special order (many will do special orders in my experience...).
Alternatively, if your pre-amp allows multiple simultaneous outputs, you can run dual pairs of XLR from your pre-amp to your amps.
Alternatively, if your pre-amp allows multiple simultaneous outputs, you can run dual pairs of XLR from your pre-amp to your amps.