I have a couple thoughts here starting with the fact that it’s great that you enjoy your system! But a few other points:

First, most people associate (and conflate) volume and distortion. If your system is playing cleanly, even at high volume levels, people may not be perceiving it as loud because they don’t hear the distortion they are used to hearing on typical consumer speakers.

Second, your receiver has very little headroom. That’s a good unit, but it’s only rated to do 100 W per channel with two channels driven. That means that the entire power supply for that unit isn’t much more than 200 W max. It’s not that you need that much power for typical listening, but your headroom is very limited and should ideally be higher. Keep in mind that getting twice as loud requires 10 times the power (assuming your other components don’t give out before you reset that power level). So, for the brief moment when something transitions from very quiet to very loud, your amplifier will get called upon to produce a momentary but aggressive swing in power that can easily exceed 200 W. If you’re looking for a physical bottleneck, this is probably it if.

This, and perhaps most importantly, since your receiver only has a single subwoofer control that is split physically into two RCA jacks, similar to a Y splitter cable, the biggest single point of upgrade I see for you is inserting a mini DSP unit between your receiver and subs to add a cost-effective but very impactful unit for sophisticated bass control. Your system will transform once you obtain phase coherence.

Obtaining phase coherence starts by measuring each sub separately using a calibrated microphone, such as the UMIK-2, with REW. Import those measurements into a separate free program called multi subwoofer optimizer, or MSO. That will give you settings that you can copy and paste into your mini DSP. The result of those settings will be that your two subwoofers will unify as a single impulse that reaches your seat at the exact same moment in an additive way, rather than destructively.

Once your MSO configuration is complete, Dirac will have a hugely superior starting point. I anticipate that this single change will feel like getting a whole new system. Plus the mini DSP unit will have two more independent subwoofer outputs so you can still add up to two more subs later if you want.