Depends on placement. I would run the two that are most symmetrical to the LP(for example two in the front corners) off a splitter as sw 1. Then run the third as sw2.
Thank youOr you could use a MiniDSP 2x4 to consolidate all subs onto one channel into the AVR. One advantage of this approach is that the 2x4 can be used to time-align the subs as well as apply pre-calibration PEQ. Here is a link to a guide on how to do this:
https://www.dropbox.com/s/w7jmpozner6muzw/MiniDSP 2x4 Set-Up Guide Latest Version.pdf?dl=1