If crossed over as opposed to the mains full range, that would still reduce the strain on the receiver. Not saying an AVR can't drive 4Ohm speakers either, just that it WILL strain it more than a comparable 8 Ohm speaker. I'm doing it too, so it can be done, but my word of caution to the OP is not to push it until you
know it can handle it. If my Marantz has a problem with it, I have another external amp I can use instead
I have a Salamander Synergy rack too.