AVR and Two Subwoofers
You can certainly use a signal splitter to send the AVR's main subwoofer output to two substhe line-level input impedance of most subs (including the Impact 10) is high enough that connecting two in parallel won't cause any problems with signal level. I'm not sure why you specify three splitters, except that you might be thinking about using both the Left and Right inputs of both subs. This is not necessary, since these inputs are summed internally, so you only need to connect one of them to the sub output from the AVR.
You could use the AVR's Zone 2 output for the second sub, but you'd have to manage the Zone 2 signalthat is, make sure it's assigned to the same source as the main zone, deal with volume, etc.which, in my opinion, is more trouble than it's worth. Using a single splitter from the main sub output to one of the inputs on each sub will work just fine.
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