Please don't be offended, but you are asking a uninformed question. Let me try to help.
First, there is almost no such thing as a 4 Ohm speaker.
Second, you don't have a 725W receiver.
Third, Speaker power ratings are basically irrelevant advertising BS.
Speakers have complex impedance. "4 Ohm nominal" may dip well below 4. Is that safe? As was suggested, it matters entirely on the speaker, listening level, and the stability of the amplifier. Amplifiers do not like high current. They get unstable and the distortion skyrockets into low impedance. Unstable is bad as about the time it starts to oscillate at ultrasonic frequencies and you head over to turn it off, the outputs all blow. ( Give us back our 16 Ohm speakers!) An AVR will have a weak power supply ( size and weight, that is the way it is) so it's ability to actually produce the rated power is not real. The Sony is plenty large enough, so I would not worry about it. I would worry about "nominal 4 Ohm" speakers. They are just a bad design. Almost all AVR's spec at 6, just to be safe. AVR's are just not designed for high currents. One good bit of news is that most moders AVRs have pretty good protection circuits, so they may shut down before they blow up. Repeat, MAY.
The only thing that matters is if playing it as you intend, how does it sound? If you try to use too much power, the supply will collapse and it will clip at a lower level. If the speakers won't produce sufficient SPL safely, they may blow. Most speakers are at least 84 dB 1M, 1W so obtaining SPL that will not cause permanent damage to your hearing only takes a few watts. The rest is for dynamics. Blowing a speaker in a home required an accident or stupidity. We buy big amps for lower distortion and stability, not for louder.
I am all in favor of quality subs. Not just MORE bass, but lower distortion bass, and by taking the bass load off the mains, you take the load off the amp too. WIN-WIN.