Which should cover the distance...XLRs or speaker cables?

Looking for advice on which cable to make the longer run, XLR or speaker cable?  I will be driving Klipschorns sitting about 18 feet apart with sources/preamp located on an adjacent wall about 10 feet from the left speaker, rather than between them.  I have to decide whether to put the monoblock amps close to the speakers with longer line level runs, or close to the preamp with longer speaker cable runs.  The environment has relatively low potential for electromagnetic interference.

Preamp is a Mytek Brooklyn Bridge with 75 ohm output impedance
Amps are Bob Carver 350 monoblocks with 100k ohm input impedance

Amps can be placed adjacent to the speakers, adjacent to the preamps, or anywhere inbetween.  My objective is to have the lowest possible noise floor.