Monoblocks fall into the vertical bi-amp camp. You’re looking to add second set of monoblocks in a horizontal bi-amp scenario. Level matching between amps will likely be an issue unless both amps have the same gain or a method to adjust gain. As mentioned, that’s a potential issue that will need a solution before proceeding.
The splitters should be fine. I successfully use similar splitter to what you linked in a horizontal bi-amp setup connected to a preamp, but my second amp has gain adjustment.
