Hi Rajan,
You have an unusual design requirement. At first blush the Stagepas 400i PA speakers are part of a dedicated PA System designed to be driven by it's own mixer/amplifier. So I'm assuming you aren't going to use that in your living room HT setup, as neither of the AVRs you list have any pre-outs to plug into the Stagepas' mixer/amplifier.
So that leaves you with driving the Stagepas speakers with one of the AVRs. The Denon manual says 6 to 16 Ohm loads so you could have some issues with the 4 ohm rated Stagepas speakers.
As I don't know where you live. Here's what is in the Onkyo TX-NR626 manual in this regard:
Speaker Connection Precautions • (North American and Taiwanese models) You can connect speakers with an impedance of between 6 and 16 ohms. If you use speakers with a lower impedance, and use the amplifier at high volume levels for a long period of time, the built-in amp protection circuit may be activated. • (European, Australian and Asian models) You can connect speakers with an impedance of between 4 and 16 ohms. If the impedance of any of the connected speakers is 4 ohms or more, but less than 6 ohms, be sure to set the minimum speaker impedance to “4ohms” (➔ page 55). If you use speakers with a lower impedance, and use the amplifier at high volume levels for a long period of time, the built-in protection circuit may be activated. • Unnecessarily long, or very thin speaker cables may affect the sound quality and should be avoided.
I suggest you test the Onkyo TX-NR626 with just the 2 Stagepas speakers connected as a stereo pair (Left & Right Front Speakers). For what I can tell they have a 1/4 inch phone plugs as an input so you'll have to make up some cables to suit. (Make sure to get the phasing correct.) Use a typical (but decent quality) source,, and select All Channel Stereo listening mode on the Onkyo. Very gradually turn up the volume and see if you like the sound you hear. Don't crank it up fast. The Stagepas speaker Specs really don't matter now as you already have them. And frankly I doubt if many on this Forum have ever heard them. (I haven't.) If you like the sound then you'll want to move on; if you don't like it you'll be looking for another solution.
If that works for you, then the folks here can chime in and assist on the rest of the system.
I hope this is helpful.