The reason for the EP500 over the EP175 is to have something that plays lower with more authority. For most music it’s output is total overkill as is any other really good subwoofer which is why having it turned up will give you way to much deep bass.
Are you having this problem when listening to music in 5.1/7.1 or are you just using 2.1. If it sounds fine in 5/7.1 but not 2.1 then there is probably an menu option in the receiver to set up 2ch stereo + sub. You may need to change the setting here to match what you’ve set for 5/7.1.
If the sub sounds to weak after using your SPL meter and calibration disk then you may just be someone who likes a lot of bass. The calibration gives you a good starting point but many people tweak the final setting to taste from there. However, before automatically tweaking everything It’s often beneficial to use the base settings for a while as you may actually like them realizing you actually had to much bass before.
I mentioned placement before and should reiterate that sub and seating placement are the first places to start when calibrating your system. You may not have much placement flexibility but if you do the first try finding the best location for the subwoofer.
If you haven’t already read them here are several articles here that can help you setup your subwoofer and integrate it to the rest of your system.
Articles This one for placement:
How to Find the Best Place for Your Subwoofer
